SIGNAL CONDITION PRINCIPLE:
1. Changing the Signal Level
2. Linearization
3. Conversion
4. Filters and Impedance Adjustments
5. Concept of Loading
6. Dynamic object in blocking recipients and inverters
Changing Signal Level:
1. Strengthening
2. Damping
3. Dynamic object stabilization
Considerations in selecting amplifiers and e- IC :
The input impedance offered to the sensor (or other element that functions as input)
Reinforcement frequency response and responsive reliability of components.
e-IC as control controller and signal conditioning process
In electronics, signal conditioning is the manipulation of an analog signal in such a way that it meets the requirements of the next stage for further processing.
In an analog-to-digital converter application, signal conditioning includes voltage or current limiting and anti-aliasing filtering.
In control engineering applications, it is common to have a sensing stage (which consists of a sensor), a signal conditioning stage (where usually amplification of the signal is done) and a processing stage (normally carried out by an ADC and a micro-controller). Operational amplifiers (op-amps) are commonly employed to carry out the amplification of the signal in the signal conditioning stage. In some transducers this feature will come inherent for eg in hall effect sensors.
In power electronics, before processing the input sensed signals by sensors like voltage sensor and current sensor, signal conditioning scales signals to level acceptable to the microprocessor.
Signal inputs accepted by signal conditioners include DC voltage and current, AC voltage and current, frequency and electric charge. Sensor inputs can be accelerometer, thermocouple, thermistor, resistance thermometer, strain gauge or bridge, and LVDT or RVDT. Specialized inputs include encoder, counter or tachometer, timer or clock, relay or switch, and other specialized inputs. Outputs for signal conditioning equipment can be voltage, current, frequency, timer or counter, relay, resistance or potentiometer, and other specialized outputs.
Signal conditioning can include amplification, filtering, converting, range matching, isolation and any other processes required to make sensor output suitable for processing after conditioning.
Filtering
Filtering is the most common signal conditioning function, as usually not all the signal frequency spectrum contains valid data. The common example is 50/60 Hz AC power lines, present in most environments, which cause noise if amplified.Amplification
Signal amplification performs two important functions: increases the resolution of the input signal, and increases its signal-to-noise ratio.[citation needed] For example, the output of an electronic temperature sensor, which is probably in the millivolts range is probably too low for an analog-to-digital converter (ADC) to process directly.[citation needed] In this case it is necessary to bring the voltage level up to that required by the ADC.Commonly used amplifiers used for signal conditioning include sample and hold amplifiers, peak detectors, log amplifiers, antilog amplifiers, instrumentation amplifiers and programmable gain amplifiers.
Attenuation
Attenuation, the opposite of amplification, is necessary when voltages to be digitized are beyond the ADC range. This form of signal conditioning decreases the input signal amplitude so that the conditioned signal is within ADC range. Attenuation is typically necessary when measuring voltages that are more than 10 V.Excitation
External power is required for the operation of an active sensor. (E.g. a temperature sensor like a thermistor & RTD, a pressure sensor(piezo-resistive and capacitive), etc.). The stability and precision of the excitation signal directly relates to the sensor accuracy and stability.Linearization
Linearization is necessary when sensors produce voltage signals that are not linearly related to the physical measurement. Linearization is the process of interpreting the signal from the sensor and can be done either with signal conditioning or through software.Electrical Isolation
Signal isolation may be used to pass the signal from the source to the measuring device without a physical connection. It is often used to isolate possible sources of signal perturbations that could otherwise follow the electrical path from the sensor to the processing circuitry. In some situations, it may be important to isolate the potentially expensive equipment used to process the signal after conditioning from the sensor.Magnetic or optical isolation can be used. Magnetic isolation transforms the signal from a voltage to a magnetic field so the signal can be transmitted without physical connection (for example, using a transformer). Optical isolation works by using an electronic signal to modulate a signal encoded by light transmission (optical encoding). The decoded light transmission is then used for input for the next stage of processing.
Surge protection
A surge protector absorbs voltage spikes to protect the next stage from damage.Automatic control has played a very important role, in the development of science and technology such as developments in the arrangement of spacecraft; missile; aircraft control system.
Similarly, the regulatory system has become an important and integrated part of processes in modern modern industries:
1. As a pressure controller
2. As a temperature controller
3. As a humidity controller
4. Flow systems in industrial processes
Control activities and monitoring that are commonly carried out by humans can be replaced by applying the principle of automation. Control activities that are carried out repeatedly, lack of precision in reading data, and the risks that may arise from a controlled system further strengthen the position of the tool / machine to control automatically.
These automatic control devices are very useful for humans. Especially if coupled with an intelligence through the programs implanted in the system will further alleviate human tasks. However, as smart as a machine, it certainly still requires the role of humans to regulate and control these devices. Automation control is not to completely replace the human role, but reduces the role and alleviates human tasks in controlling a process.
With the development of technology, the subject of the Control Engineering System course provides convenience in:
1. Get performance from a Dynamic system,
2. Can enhance production quality
3. Reducing production costs,
4. Increasing the rate of production,
5. And eliminate routine work that is boring, which must be done by humans.
The Basic Concept of Controller :
The system setting (signal conditioning) technique is carried out based on the basics of "feedback" techniques and linear analysis of the system.
So by including the concepts of network theory (Network theory) will get an analysis of system settings and controls on the desired output (output).
Thus in the problem of "Technical System Analysis" the problem will be discussed:
• System and model of the system, also the mathematical formulation of the system that is reviewed and how to solve it.
• For feedback techniques (feedback) is one of the most basic processes and almost exists in all dynamic systems, among others:
- Matters relating to the human self
- Relationship between humans and machines
- Equipment that supports each other.
So that due to the theory of feedback control systems will continue to develop as a particular scientific discipline, and will be useful for analyzing and designing a practical control system for other technological devices.
In order to be able to understand in the above, it is necessary to understand the knowledge of the basics of science, including:
• Fundamentals of physics
• Calculus basics
• The basics of mathematics
• Electrical and mechanical components and character.
So that the necessary mathematical tools include various topics including:
• Settlement of problems with differential and integral equations
• Laplace transform and complex variables.
The control system is classified into 2, namely:
1. "Open loop system" is a sustu system whose control measures are free of output.
The advantages:
- The construction is simple
- Cheaper than a closed system
- There are no problems with instability
- Accuracy of work is determined by caliber
The disadvantages:
- Interference and calinberation changes, will cause an error, so the output is not as desired.
- To maintain the required quality at the output, repeated calibration is required at any given time.
2. "Closed Loop System" Control System, is a system whose control measures depend on the output.
Its characteristics include:
- Able to improve accuracy, so that it can continue to reproduce its input.
- Can reduce the sensitivity of the comparison of entry to input for changes in system characteristics.
- Reduces the effect of linearity and distortion.
So the system is a combination of several components that work together and can carry out certain tasks including:
- Electrical system
- Mechanical System
- Thermic system
- Biological system
- The system of everyday human life
- Communication systems and object information in electronic media
- Etc.
Thus the system of controls (feetback control system): namely a system where the instantaneous price of the output, is always assessed and compared with the input, thus producing the desired output.
As a result, thus the input minus "Output" will produce a driving signal will result in "Signal Error" that regulates the system, so as to produce the desired Output.
Problems in the control system
The main point in the system analysis in the synthesis of a control system, among others:
1. Transient period: i.e. each control system is expected to have as little transient time as possible, meaning that it can be as short as possible, so that the output price is in accordance with the desired. Staying with a small transient time, the output will have a large deviation and or oscillation in the direction of a higher yana price (increasing).
2. Steady state time (after the symptoms of the transition are considered complete), here are two very important things, namely:
a. The error (steady state error) is that the output is actually not the same as the desired output.
b. The magnitude of the steady state error errors of the two systems is strongly influenced by the "type system" and the type of "input"
3. Stability: That is, a system determines whether the system has magnitude (especially its output) at a price that is very large or outside the limits of our assessment.
The main point in the system analysis in the synthesis of a control system, among others:
1. Transient period: i.e. each control system is expected to have as little transient time as possible, meaning that it can be as short as possible, so that the output price is in accordance with the desired. Staying with a small transient time, the output will have a large deviation and or oscillation in the direction of a higher yana price (increasing).
2. Steady state time (after the symptoms of the transition are considered complete), here are two very important things, namely:
a. The error (steady state error) is that the output is actually not the same as the desired output.
b. The magnitude of the steady state error errors of the two systems is strongly influenced by the "type system" and the type of "input"
3. Stability: That is, a system determines whether the system has magnitude (especially its output) at a price that is very large or outside the limits of our assessment.
4. objects and instruments that move in different spaces and times
Fig 1. The example of control dynamic with concept signal conditioner
Fig 2 . The monitoring Tank with the sensor for signal conditioner over
BASIC TERMINOLOGY
• Modeling
• Explicit solutions
• Numerical solutions
• Empirical data
• Simulation
• Lumped parameter (masses and springs)
• Distributed parameters (stress in a solid)
• Continuous vs. Discrete
• Linear vs. Non-linear
• linearity and superposition
• reversibility
• through and across variables
• Analog vs. Digital
• process vs. controllers
• Basic system categories
. control system types: servo vs. regulating/process control
• open loop vs. closed loop
• disturbances
• component variations
• system error
• analysis vs. design
• mechatronics
• embedded systems
• real-time systems
EXAMPLE SYSTEM
• Servo control systems
• Robot
TRANSLATION IN INTRODUCTION :
If the velocity and acceleration of a body are both zero then the body will be static.
If the applied forces are balanced, and cancel each other out, the body will not accelerate.
If the forces are unbalanced then the body will accelerate. If all of the forces act through
the center of mass then the body will only translate. Forces that do not act through the center
of mass will also cause rotation to occur. This chapter will focus only on translational
systems.
These state simply that velocity is the first derivative of position, and velocity is the first derivative of
acceleration. Conversely the acceleration can be integrated to find velocity, and the velocity
can be integrated to find position. Therefore, if we know the acceleration of a body, we
can determine the velocity and position. Finally, when a force is applied to a mass, an
acceleration can be found by dividing the net force by the mass.
MISSION :
• To be able to develop differential equations that describe translating systems.
• Basic laws of motion
• Gravity, inertia, springs, dampers, cables and pulleys, drag, friction, FBDs
• System analysis techniques
• Design case
MODELING
When modeling translational systems it is common to break the system into parts.
These parts are then described with Free Body Diagrams (FBDs). Common components
that must be considered when constructing FBDs are listed below, and are discussed in
following sections.
• gravity and other fields - apply non-contact forces
• inertia - opposes acceleration and deceleration
• springs - resist deflection
• dampers and drag - resist motion
• friction - opposes relative motion between bodies in contact
. cables and pulleys - redirect forces
• contact points/joints - transmit forces through up to 3 degrees of freedom
Free Body Diagrams
Free Body Diagrams (FBDs) allow us to reduce a complex mechanical system into
smaller, more manageable pieces. The forces applied to the FBD can then be summed to
provide an equation for the piece. These equations can then be used later to do an analysis
of system behavior. These are required elements for any engineering problem involving
rigid bodies.
Mass and Inertia
In a static system the sum of forces is zero and nothing is in motion. In a dynamic
system the sum of forces is not zero and the masses accelerate. The resulting imbalance in
forces acts on the mass causing it to accelerate. For the purposes of calculation we create a
virtual reaction force, called the inertial force. This force is also known as D’Alembert’s
(pronounced as daa-lamb-bears) force. It can be included in calculations in one of two
ways.The first is to add the inertial force to the FBD and then add it into the sum of The second method is known as D’Alembert’s equation where all of the forces are summed and set equal to the inertial force.
Gravity and Other Fields
Gravity is a weak force of attraction between masses. In our situation we are in the
proximity of a large mass (the earth) which produces a large force of attraction. When analyzing
forces acting on rigid bodies we add this force to our FBDs. The magnitude of the
force is proportional to the mass of the object, with a direction toward the center of the
earth (down). The relationship between mass and force is clear in the metric system with mass
having the units Kilograms (kg), and force the units Newtons (N). The relationship
between these is the gravitational constant 9.81N/kg, which will vary slightly over the surface
of the earth. The Imperial units for force and mass are both the pound (lb.) which
often causes confusion. To reduce this confusion the unit for force is normally modified to
be, lbf.
Springs
Springs are typically constructed with elastic materials such as metals and plastics,
that will provide an opposing force when deformed. The properties of the spring are determined
by the Young’s modulus (E) of the material and the geometry of the spring.
Damping and Drag
A damper is a component that resists motion. The resistive force is relative to the
rate of displacement. As mentioned before, springs store energy in a system but dampers
dissipate energy. Dampers and springs are often used to compliment each other in designs.
Damping can occur naturally in a system, or can be added by design.
Cables And Pulleys
Cables are useful when transmitting tensile forces or displacements. The center line
of the cable becomes the centerline for the force. And, if the force becomes compressive,
the cable becomes limp, and will not transmit force. A cable by itself can be represented as
a force vector. When used in combination with pulleys, a cable can redirect a force vector
or multiply a force.
Typically we assume that a pulley is massless and frictionless (in the rotation chapter
we will assume they are not).
Friction
Viscous friction was discussed before, where a lubricant would provide a damping
effect between two moving objects. In cases where there is no lubricant, and the touching
surfaces are dry, dry coulomb friction may result. In this case the surfaces will stick in
place until a maximum force is overcome. After that the object will begin to slide and a
constant friction force will result.
Contact Points And Joints
A system is built by connecting components together. These connections can be
rigid or moving. In solid connections all forces and moments are transmitted and the two
pieces act as a single rigid body. In moving connections there is at least one degree of freedom.
If we limit this to translation only, there are up to three degrees of freedom, x, y and
z. In any direction there is a degree of freedom, a force or moment cannot be transmitted.
When constructing FBDs for a system we must break all of the components into
individual rigid bodies. Where the mechanism has been broken the contact forces must be
added to both of the separated pieces.
SYSTEM EXAMPLES
An orderly approach to system analysis can simplify the process of analyzing large
systems. The list of steps below is based on general observations of good problem solving
techniques.
1. Assign letters/numbers to designate force components (if not already done) -
this will allow you to refer to components in your calculations.
2. Define positions and directions for any moving masses. This should include the
selection of reference points.
3. Draw free body diagrams for each component, and add forces (inertia is
optional).
4. Write equations for each component by summing forces.
5. Combine the equations by eliminating unwanted variables.
6. Develop a final equation that relates input (forcing functions) to
outputs (results).
I . ANALYSIS OF DIFFERENTIAL EQUATIONS
Tobe Know :
• First and second-order homogeneous differential equations
• Non-homogeneous differential equations
• First and second-order responses
• Non-linear system elements
• Design case
MISSION :
• To develop explicit equations that describe a system response.
• To recognize first and second-order equation forms.
we derived differential equations of motion for translating
systems. These equations can be used to analyze the behavior of the system and make
design decisions. The most basic method is to select a standard input type (a forcing function)
and initial conditions, and then solve the differential equation. differential the same wit timing or timer in electronic work .
Solving a differential equation results in an explicit solution. This equation provides
the general response as a function of time, but it can also be used to find frequencies
and other characteristics of interest. This section will review techniques used to integrate
first and second-order homogenous differential equations. These equations correspond to
systems without inputs, also called unforced systems.
RESPONSES
Solving differential equations tends to yield one of two basic equation forms. The
e-to-the-negative-t forms are the first-order responses and slowly decay over time. They
never naturally oscillate, and only oscillate if forced to do so. The second-order forms may
include natural oscillation.
First-order
A first-order system is described with a first-order differential equation. The
response function for these systems is natural decay or growth .
Second-order
A second-order system response typically contains two first-order responses, or a
first-order response and a sinusoidal component .
Other Responses
First-order systems have e-to-the-t type responses. Second-order systems add
another e-to-the-t response or a sinusoidal excitation. As we move to higher order linear
systems we typically add more e-to-the-t terms, and/or more sinusoidal terms.
In some cases we will have systems with multiple differential equations, or nonlinear
terms. In these cases explicit analysis of the equations may not be feasible
RESPONSE ANALYSIS
Up to this point we have mostly discussed the process of calculating the system
response. As an engineer, obtaining the response is important, but evaluating the results is
more important. The most critical design consideration is system stability. In most cases a
system should be inherently stable in all situations, such as a car "cruise control". In other
cases an unstable system may be the objective, such as an explosive device .
Simple methods
for determining the stability of a system are listed below:
1. If a step input causes the system to go to infinity, it will be inherently unstable.
2. A ramp input might cause the system to go to infinity; if this is the case, the system
might not respond well to constant change.
3. If the response to a sinusoidal input grows with each cycle, the system is probably
resonating, and will become unstable.
Beyond establishing the stability of a system, we must also consider general performance.
This includes the time constant for a first-order system, or damping coefficient
and natural frequency for a second-order system. For example, assume we have designed
an elevator that is a second-order system. If it is under damped the elevator will oscillate,
possibly leading to motion sickness, or worse. If the elevator is over damped it will take
longer to get to floors. If it is critically damped it will reach the floors quickly, without
overshoot.
Engineers distinguish between initial setting effects (transient) and long term
effects (steady-state). The transient effects are closely related to the homogeneous solution
to the differential equations and the initial conditions. The steady-state effects occur after
some period of time when the system is acting in a repeatable or non-changing form. Figure
3.30 shows a system response. The transient effects at the beginning include a quick
rise time and an overshoot. The steady-state response settles down to a constant amplitude
sine wave.
NON-LINEAR SYSTEMS
Non-linear systems cannot be described with a linear differential equation. A basic
linear differential equation has coefficients that are constant, and the derivatives are all
first order.
Non-Linear Differential Equations
A non-linear differential equation is description as like as It involves a person
ejected from an aircraft with a drag force coefficient of 0.8. (Note: This coefficient is calculated
using the drag coefficient and other properties such as the speed of sound and
cross sectional area.) The FBD shows the sum of forces, and the resulting differential
equation. The velocity squared term makes the equation non-linear, and so it cannot be
analyzed with the previous methods. In this case the terminal velocity is calculated by setting
the acceleration to zero. This results in a maximum speed of 126 kph. The equation can also be solved using explicit integration .
Non-Linear Equation Terms
If our models include a device that is non-linear and we want to use a linear technique to solve the equation, we will need to linearize the model before we can proceed. A
non-linear system can be approximated with a linear equation using the following method.
1. Pick an operating point or range for the component.
2. Find a constant value that relates a change in the input to a change in the output.
3. Develop a linear equation.
4. Use the linear equation for the analysis.
A linearized differential equation can be approximately solved using known techniques
as long as the system doesn’t travel too far from the linearized point. The example
in Figure 3.36 shows the linearization of a non-linear equation about a given operating
point. This equation will be approximately correct as long as the first derivative doesn’t
move too far from 100. When this value does, the new velocity can be calculated.
Changing Systems
In practical systems, the forces at work are continually changing. For example a
system often experiences a static friction force when motion is starting, but once motion
starts it is replaced with a smaller kinetic friction. Another example is tension in a cable.
When in tension a cable acts as a spring. But, when in compression the force goes to zero.
The values of the spring and damping coefficients can be used to select actual
components. Some companies will design and build their own components. Components
can also be acquired by searching catalogs, or requesting custom designs from other companies.
SUMMARY
• First and second-order differential equations were analyzed explicitly.
• First and second-order responses .
• analysis was brainstorming.
• A case study looked at a second-order system.
• Non-linear systems can be analyzed by making them linear.
Key points:
First-order:
find initial final values
find time constant with 63% or by slope
use these in standard equation
Second-order:
find damped frequency from graph
find time to first peak
use these in cosine equation
II. NUMERICAL ANALYSIS
INTRODUCTION
For engineering analysis it is always preferable to develop explicit equations that
include symbols, but this is not always practical. In cases where the equations are too
costly to develop, numerical methods can be used. As their name suggests, numerical
methods use numerical calculations (i.e., numbers not symbols) to develop a unique solution
to a differential equation. The solution is often in the form of a set of numbers, or a
graph. This can then be used to analyze a particular design case. The solution is often
returned quickly so that trial and error design techniques may be used. But, without a symbolic
equation the system can be harder to understand and manipulate.
This chapter focuses on techniques that can be used for numerically integrating
systems of differential equations.
THE GENERAL METHOD
The general process of analyzing systems of differential equations involves first
putting the equations into standard form, and then integrating these with one of a number
of techniques. State variable equations are the most common standard equation form. In
this form all of the equations are reduced to first-order differential equations. These firstorder
equations are then easily integrated to provide a solution for the system of equations.
MISSION :
• To be able to solve systems of differential equations using numerical methods.
• State variable form for differential equations
• Numerical integration with software and calculators
• Numerical integration theory: first-order, Taylor series and Runge-Kutta
• Using tabular data
• A design case
State Variable Form
At any time a system can be said to have a state. Consider a car for example, the
state of the car is described by its position and velocity. Factors that are useful when identifying
state variables are:
• The variables should describe energy storing elements (potential or kinetic).
• The variables must be independent.
• They should fully describe the system elements.
After the state variables of a system have been identified, they can be used to write
first-order state variable equations.
NUMERICAL INTEGRATION ( RESET NUMERIC IN Electronic Work )
Repetitive calculations can be used to develop an approximate solution to a set of
differential equations. Starting from given initial conditions, the equation is solved with
small time steps. Smaller time steps result in a higher level of accuracy, while larger time
steps give a faster solution.
Numerical Integration With Tools
Numerical solutions can be developed with hand calculations, but this is a very
time consuming task. In this section we will explore some common tools for solving state
variable equations. The analysis process follows the basic steps listed below.
1. Generate the differential equations to model the process.
2. Select the state variables.
3. Rearrange the equations to state variable form.
4. Add additional equations as required.
5. Enter the equations into a computer or calculator and solve.
Numerical Integration
The simplest form of numerical integration is Euler’s first-order method. Given the
current value of a function and the first derivative, we can estimate the function value a
short time later,
Taylor Series
First-order integration works well with smooth functions. But, when a highly
curved function is encountered we can use a higher order integration equation.
Runge-Kutta Integration
First-order integration provides reasonable solutions to differential equations. That
accuracy can be improved by using higher order derivatives to compensate for function
curvature. The Runge-Kutta technique uses first-order differential equations (such as state
equations) to estimate the higher order derivatives, thus providing higher accuracy without
requiring other than first-order differential equations.
SYSTEM RESPONSE
In most cases the result of numerical analysis is graphical or tabular.
In both cases details such as time constants and damped frequencies can be obtained by the same methods used for experimental analysis. In addition to these methods there is a technique that
can determine the steady-state response of the system.
Steady-State Response
The state equations can be used to determine the steady-state response of a system
by setting the derivatives to zero, and then solving the equations.
DIFFERENTIATION AND INTEGRATION OF EXPERIMENTAL DATA
When doing experiments, data is often collected in the form of individual data
points (not as complete functions). It is often necessary to integrate or differentiate these
values.
III . ADVANCED CONTROL DYNAMIC
Switching Functions
When analyzing a system, we may need to choose an input that is more complex
than inputs such as steps, ramps, sinusoidal and parabolic. The easiest way to do this is to
use switching functions. Switching functions turn on (have a value of 1) when their arguments are greater than or equal to zero, or off (a value of 0) when the argument is negative.
Examples of the use of switching functions .
Interpolating Tabular Data
In some cases we are given tables of numbers instead of equations for a system
component. These can still be used to do numerical integration by calculating coefficient
values as required, in place of an equation. Tabular data consists of separate data points
Modeling Functions with Splines
When greater accuracy is required, smooth curves can be fitted to interpolate
points. These curves are known as splines. There are multiple methods for creating
splines, but the simplest is to use a polynomial fitted to a set of points.
Non-Linear Elements
Despite our deepest wishes for simplicity, most systems contain non-linear components.
In the last chapter we looked at dealing with non-linearities by linearizing them
locally. Numerical techniques will handle non-linearities easily, but smaller time steps are
required for accuracy. Consider the mass and an applied force .
SUMMARY
• State variable equations are used to reduced to first order differential equations.
• First order equations can be integrated numerically.
• Higher order integration, such as Runge-Kutta increase the accuracy.
• Switching functions allow functions terms to be turned on and off to provide
more complex function.
• Tabular data can be used to get numerical values.
IV . ROTATION
INTRODUCTION
The equations of motion for a rotating mass Given the angular position, the angular velocity can be found by differentiating once, the angular acceleration can be found by differentiating again. The angular acceleration can be integrated to find the angular velocity, the angular velocity can be integrated to find the angular position. The angular acceleration is proportional to an applied torque, but inversely
proportional to the mass moment of inertia.
Basic properties of rotation
MISSION :
• To be able to develop and analyze differential equations for rotational systems.
• Basic laws of motion
• Inertia, springs, dampers, levers, gears and belts
• Design case
MODELING
Free Body Diagrams (FBDs) are required when analyzing rotational systems, as
they were for translating systems. The force components normally considered in a rotational
system include,
• inertia - opposes acceleration and deceleration
• springs - resist deflection
• dampers - oppose velocity
• levers - rotate small angles
• gears and belts - change rotational speeds and torques
Inertia
When unbalanced torques are applied to a mass it will begin to accelerate, in rotation.
The sum of applied torques is equal to the inertia forces .
The mass moment of inertia determines the resistance to acceleration. This can be
calculated using integration, or found in tables. When dealing with rotational acceleration
it is important to use the mass moment of inertia, not the area moment of inertia.
The center of rotation for free body rotation will be the centroid. Moment of inertia
values are typically calculated about the centroid. If the object is constrained to rotate
about some point, other than the centroid, the moment of inertia value must be recalculated.
Springs
Twisting a rotational spring will produce an opposing torque. This torque increases
as the deformation increases. The spring constant for a torsional spring will be relatively constant, unless the
material is deformed outside the linear elastic range, or the geometry of the spring changes
significantly.
When dealing with strength of material properties the area moment of inertia is
required. The calculation for the area moment of inertia is similar to that for the mass
moment of inertia.
Damping
Rotational damping is normally caused by viscous fluids, such as oils, used for
lubrication. The first equation is used for a system with one rotating and one stationary part. The second equation is used for damping between two rotating parts.
Levers
The lever can be used to amplify forces or motion. Although
theoretically a lever arm could rotate fully, it typically has a limited range of motion. The
amplification is determined by the ratio of arm lengths to the left and right of the center.
Gears and Belts
While levers amplify forces and motions over limited ranges of motion, gears can
rotate indefinitely. Some of the basic gear forms are listed below.
Spur - Round gears with teeth parallel to the rotational axis.
Rack - A straight gear (used with a small round gear called a pinion).
Helical - The teeth follow a helix around the rotational axis.
Bevel - The gear has a conical shape, allowing forces to be transmitted at angles.
Gear teeth are carefully designed so that they will mesh smoothly as the gears
rotate. The forces on gears acts at a tangential distance from the center of rotation called
the pitch diameter. In the transmission the gear ratio
is changed by sliding (left-right) some of the gears to change the sequence of gears transmitting
the force.
Friction
Friction between rotating components is a major source of inefficiency in
machines. It is the result of contact surface materials and geometries. Calculating friction
values in rotating systems is more difficult than translating systems. Normally rotational
friction will be given as static and kinetic friction torques. Basically
these problems require that the model be analyzed as if the friction surface is fixed. If the
friction force exceeds the maximum static friction the mechanism is then analyzed using
the dynamic friction torque. There is friction between the shaft and the hole in the wall.
The friction force is left as a variable for the derivation of the state equations. The friction
value must be calculated using the appropriate state equation. The result of this calculation
and the previous static or dynamic condition is then used to determine the new friction
value.
Permanent Magnet Electric Motors
DC motors create a torque between the rotor (inside) and stator (outside) that is
related to the applied voltage or current. In a permanent magnet motor there are magnets
mounted on the stator, while the rotor consists of wound coils. When a voltage is applied
to the coils the motor will accelerate. The speed response of a permanent magnet DC motor is first-order.
SUMMARY
• The basic equations of motion were execute .
• Mass and area moment of inertia are used for inertia and springs.
• Rotational dampers and springs.
• A design case was presented.
IV . INPUT-OUTPUT EQUATIONS
INTRODUCTION
To solve a set of differential equations we have two choices, solve them numerically
or symbolically. For a symbolic solution the system of differential equations must be
manipulated into a single differential equation. In this chapter we will look at methods for
manipulating differential equations into useful forms.
THE DIFFERENTIAL OPERATOR
The differential operator ’d/dt’ can be written in a number of forms. In this book
there have been two forms used thus far, d/dt x and x-dot. For convenience we will add a
third, ’D’. The basic definition of this operator, and related operations . In basic terms the operator can be manipulated as if it is a normal variable. Multiplying
by ’D’ results in a derivative, dividing by ’D’ results in an integral. The first-order
axiom can be used to help solve a first-order differential equation.
MISSION :
• To be able to develop input-output equations for mechanical systems.
• The differential operator, input-output equations
• Design case - vibration isolation
Converting Input-Output Equations to State Equations
In some instances we will want to numerically integrate an input-output equation.
Integrating Input-Output Equations
An input-output equation is already in a form suitable for normal integration techniques,
with the left hand side being the homogeneous part, and the right hand side is the
particular part. If the non homogeneous part includes derivatives, these determine the values
of initial conditions.
DESIGN CASE
The classic mass-spring-damper system is shown in Figure 6.13. In this example
the forces are summed to provide an equation. The differential operator is replaced, and
the equation is manipulated into transfer function form. The transfer function is given in
two different forms because the system is reversible and the output could be either ’F’ or
’x’.
SUMMARY
• The differential operator can be manipulated algebraically
• Equations can be manipulated into input-output forms and solved as normal differential
equations
V . ELECTRICAL SYSTEMS
MISSION :
• To apply analysis techniques to circuits
• Basic components; resistors, power sources, capacitors, inductors and op-amps
• Device impedance
• Example circuits
INTRODUCTION
A voltage is a pull or push acting on electrons. The voltage will produce a current
when the electrons can flow through a conductor. The more freely the electrons can flow,
the lower the resistance of a material. Most electrical components are used to control this
flow.
MODELING
Kirchoff’s voltage and current laws : The node current law
holds true because the current flow in and out of a node must total zero. If the sum of currents
was not zero then electrons would be appearing and disappearing at that node, thus
violating the law of conservation of matter. The loop voltage law states that the sum of all
rises and drops around a loop must total zero.
The simplest form of circuit analysis is for DC circuits, typically only requiring
algebraic manipulation. In AC circuit analysis we consider the steady-state response to a
MISSION
• To apply analysis techniques to circuits
• Basic components; resistors, power sources, capacitors, inductors and op-amps
• Device impedance
sinusoidal input. Finally the most complex is transient analysis, often requiring integration,
or similar techniques.
• DC (Direct Current) - find the response for a constant input.
• AC (Alternating Current) - find the steady-state response to an AC input.
• Transient - find the initial response to changes.
There is a wide range of components used in circuits. The simplest components are
passive, such as resistors, capacitors and inductors. Active components are capable of
changing their behaviors, such as op-amps and transistors.
Component :
• resistors - reduce current flow as described with ohm’s law
• voltage/current sources - deliver power to a circuit
• capacitors - pass current based on current flow, these block DC currents
• inductors - resist changes in current flow, these block high frequencies
• op-amps - very high gain amplifiers useful in many forms
Voltage and Current Sources
A voltage source will maintain a voltage in a circuit, by varying the current as
required. A current source will supply a current to a circuit, by varying the voltage as
required. The schematic symbols for voltage and current sources are shown in Figure 7.5.
The supplies with ’+’ and ’-’ symbols provide DC voltages, with the symbols indicating
polarity. The symbol with two horizontal lines is a battery. The circle with a sine wave is
an AC voltage supply. The last symbol with an arrow inside the circle is a current supply.
The arrow indicates the direction of positive current flow.
Op-Amps
The ideal model of an op-amp : On the left hand side are
the inverting and non-inverting inputs. Both of these inputs are assumed to have infinite
impedance, and so no current will flow. Op-amp application circuits are designed so that
the inverting and non-inverting inputs are driven to the same voltage level. The output of
the op-amp is shown on the right. In circuits op-amps are used with feedback to perform
standard operations such as those listed below.
• adders, subtractors, multipliers, and dividers - simple analog math operations
• amplifiers - increase the amplitude of a signal
• impedance isolators - hide the resistance of a circuit while passing a voltage
Feedforward Controllers
When a model of a system is well known it can be used to improve the performance
of a control system by adding a feedforward function : PID _____.
The feedforward function is basically an inverse model of the process. When this is used
together with a more traditional feedback function the overall system can outperform
more traditional controllers function, such as the PID controller.
SUMMARY
• Transfer functions can be used to model the ratio of input to output.
• Block diagrams can be used to describe and simplify systems.
• Controllers can be designed to meet criteria, such as damping ratio and natural
frequency.
• System errors can be used to determine the long term stability and accuracy of a
controlled system.
• Other control types are possible for more advanced systems.
VI . ANALOG INPUTS AND OUTPUTS
INTRODUCTION
An analog value is continuous, not discrete : In the previous
chapters, techniques were discussed for designing continuos control systems. In this
chapter we will examine analog inputs and outputs so that we may design continuous control
systems that use computers.
Logical and Continuous Values :
Typical analog inputs and outputs for computers are listed below. Actuators and
sensors that can be used with analog inputs and outputs will be discussed in later chapters.
Inputs:
• oven temperature
• fluid pressure
• fluid flow rate
MISSION :
• To understand the basics of conversion to and from analog values.
• Analog inputs and outputs
• Sampling issues; aliasing, quantization error, resolution
OUTPUT :
. fluid valve position
• motor position
• motor velocity
type of system a physical
value is converted to a voltage, current or other value by a transducer. A signal conditioner
converts the signal from the transducer to a voltage or current that is read by the analog
input.
Analog to digital and digital to analog conversion uses integers within the computer.
Integers limit the resolution of the numbers to a discrete, or quantized range.
ANALOG INPUTS
To input an analog voltage (into a computer) the continuous voltage value must be
sampled and then converted to a numerical value by an A/D (Analog to Digital) converter
(also known as ADC). Figure 13.4 shows a continuous voltage changing over time.
ANALOG OUTPUTS
Analog outputs are much simpler than analog inputs. To set an analog output an
integer is converted to a voltage. This process is very fast, and does not experience the
timing problems with analog inputs. But, analog outputs are subject to quantization errors.
These relationships are
almost identical to those of the A/D converter.
NOISE REDUCTION
Shielding
When a changing magnetic field cuts across a conductor, it will induce a current
flow. The resistance in the circuits will convert this to a voltage.
result in erroneous readings from sensors, and signal to outputs. Shielding will reduce the
effects of the interference. When shielding and grounding are done properly, the effects of
electrical noise will be negligible. Shielding is normally used for; all logical signals in
noisy environments, high speed counters or high speed circuitry, and all analog signals.
There are two major approaches to reducing noise; shielding and twisted pairs.
Shielding involves encasing conductors and electrical equipment with metal. As a result
electrical equipment is normally housed in metal cases. Wires are normally put in cables
with a metal sheath surrounding both wires. The metal sheath may be a thin film, or a
woven metal mesh. Shielded wires are connected at one end to "drain" the unwanted signals
into the cases of the instruments.
Grounding
- ground voltages are based upon the natural voltage level in the physical ground
(the earth under your feet). This will vary over a distance. Most buildings and electrical
systems use a ground reference for the building. Between different points on the same
building ground voltage levels may vary as much as a few hundred millivolts. This can
lead to significant problems with voltage readings and system safety.
- A signal can be floating, or connected to a ground
- if floating a system normally has a self contained power source, or self reference
such as a battery, strain gauge or thermocouple. These are usually read with double ended
outputs. The potential for floating voltage levels can be minimized by connecting larger
resistors (up to 100K) from the input to ground.
- a grounded system uses a single common (ground) for all signals. These are normally
connected to a single ended inputs.
- the analog common can also be connected to the ground with a large resistor to
drain off induced voltages.
- cable shields or grounds are normally only connected at one side to prevent
ground loops.
SUMMARY
• A/D conversion will convert a continuous value to an integer value.
• D/A conversion is easier and faster and will convert a digital value to an analog
value.
• Resolution limits the accuracy of A/D and D/A converters.
• Sampling too slowly will alias the real signal.
• Analog inputs are sensitive to noise.
• Analog shielding should be used to improve the quality of electrical signals.
VII . CONTINUOUS SENSORS
INTRODUCTION
Continuous sensors convert physical phenomena to measurable signals, typically
voltages or currents. Consider a simple temperature measuring device, there will be an
increase in output voltage proportional to a temperature rise. A computer could measure
the voltage, and convert it to a temperature. The basic physical phenomena typically measured
with sensors include;
- angular or linear position
- acceleration
- temperature
- pressure or flow rates
- stress, strain or force
- light intensity
- sound
Most of these sensors are based on subtle electrical properties of materials and
devices. As a result the signals often require signal conditioners. These are often amplifiers
that boost currents and voltages to larger voltages.
Sensors are also called transducers. This is because they convert an input phenomena
to an output in a different form. This transformation relies upon a manufactured
device with limitations and imperfection. As a result sensor limitations are often character
MISSION :
• To understand the common continuous sensor types.
• To understand interfacing issues.
• Continuous sensor issues; accuracy, resolution, etc.
• Angular measurement; potentiometers, encoders and tachometers
• Linear measurement; potentiometers, LVDTs, Moire fringes and accelerometers
• Force measurement; strain gages and piezoelectric
• Liquid and fluid measurement; pressure and flow
• Temperature measurement; RTDs, thermocouples and thermistors
• Other sensors
• Continuous signal inputs and wiring
• Glossary
Objectives:
• To understand the common continuous sensor types.
• To understand interfacing issues.
INTRODUCTION
Continuous sensors convert physical phenomena to measurable signals, typically
voltages or currents. Consider a simple temperature measuring device, there will be an
increase in output voltage proportional to a temperature rise. A computer could measure
the voltage, and convert it to a temperature. The basic physical phenomena typically measured
with sensors include;
- angular or linear position
- acceleration
- temperature
- pressure or flow rates
- stress, strain or force
- light intensity
- sound
Most of these sensors are based on subtle electrical properties of materials and
devices. As a result the signals often require signal conditioners. These are often amplifiers
that boost currents and voltages to larger voltages.
Sensors are also called transducers. This is because they convert an input phenomena
to an output in a different form. This transformation relies upon a manufactured
device with limitations and imperfection. As a result sensor limitations are often characterterized with;
Accuracy - This is the maximum difference between the indicated and actual reading.
For example, if a sensor reads a force of 100N with a ±1% accuracy, then
the force could be anywhere from 99N to 101N.
Resolution - Used for systems that step through readings. This is the smallest
increment that the sensor can detect, this may also be incorporated into the
accuracy value. For example if a sensor measures up to 10 inches of linear displacements,
and it outputs a number between 0 and 100, then the resolution of
the device is 0.1 inches.
Repeatability - When a single sensor condition is made and repeated, there will be
a small variation for that particular reading. If we take a statistical range for
repeated readings (e.g., ±3 standard deviations) this will be the repeatability.
For example, if a flow rate sensor has a repeatability of 0.5cfm, readings for an
actual flow of 100cfm should rarely be outside 99.5cfm to 100.5cfm.
Linearity - In a linear sensor the input phenomenon has a linear relationship with
the output signal. In most sensors this is a desirable feature. When the relationship
is not linear, the conversion from the sensor output (e.g., voltage) to a calculated
quantity (e.g., force) becomes more complex.
Precision - This considers accuracy, resolution and repeatability or one device relative
to another.
Range - Natural limits for the sensor. For example, a sensor for reading angular
rotation may only rotate 200 degrees.
Dynamic Response - The frequency range for regular operation of the sensor. Typically
sensors will have an upper operation frequency, occasionally there will be
lower frequency limits. For example, our ears hear best between 10Hz and
16KHz.
Environmental - Sensors all have some limitations over factors such as temperature,
humidity, dirt/oil, corrosives and pressures. For example many sensors
will work in relative humidities (RH) from 10% to 80%.
Calibration - When manufactured or installed, many sensors will need some calibration
to determine or set the relationship between the input phenomena, and
output. For example, a temperature reading sensor may need to be zeroed or
adjusted so that the measured temperature matches the actual temperature. This
may require special equipment, and need to be performed frequently.
Cost - Generally more precision costs more. Some sensors are very inexpensive,
but the signal conditioning equipment costs are significant.
Encoders
Encoders use rotating disks with optical windows: The encoder contains an optical disk with fine windows etched into it. Light from emitters
passes through the openings in the disk to detectors. As the encoder shaft is rotated, the
light beams are broken.
There are two fundamental types of encoders; absolute and incremental. An absolute
encoder will measure the position of the shaft for a single rotation. The same shaft
angle will always produce the same reading. The output is normally a binary or grey code
number. An incremental (or relative) encoder will output two pulses that can be used to
determine displacement. Logic circuits or software is used to determine the direction of
rotation, and count pulses to determine the displacement. The velocity can be determined
by measuring the time between pulses.
The absolute encoder has two rings, the
outer ring is the most significant digit of the encoder, the inner ring is the least significant
digit. The relative encoder has two rings, with one ring rotated a few degrees ahead of the
other, but otherwise the same. Both rings detect position to a quarter of the disk. To add
accuracy to the absolute encoder more rings must be added to the disk, and more emitters
and detectors. To add accuracy to the relative encoder we only need to add more windows
to the existing two rings. Typical encoders will have from 2 to thousands of windows per
ring.
When using absolute encoders, the position during a single rotation is measured
directly. If the encoder rotates multiple times then the total number of rotations must be
counted separately.
When using a relative encoder, the distance of rotation is determined by counting
the pulses from one of the rings. If the encoder only rotates in one direction then a simple
count of pulses from one ring will determine the total distance. If the encoder can rotate
both directions a second ring must be used to determine when to subtract pulses. The
quadrature scheme, using two rings, is shown in Figure 14.5. The signals are set up so that
one is out of phase with the other. Notice that for different directions of rotation, input B
either leads or lags A. Interfaces for encoders are commonly available for PLCs and as purchased units. Newer PLCs will also allow two normal inputs to be used to decode encoder inputs
Normally absolute and relative encoders require a calibration phase when a controller
is turned on. This normally involves moving an axis until it reaches a logical sensor
that marks the end of the range. The end of range is then used as the zero position.
Machines using encoders, and other relative sensors, are noticeable in that they normally
move to some extreme position before use.
Tachometers
Tachometers measure the velocity of a rotating shaft. A common technique is to
mount a magnet to a rotating shaft. When the magnetic moves past a stationary pick-up
coil, current is induced. For each rotation of the shaft there is a pulse in the coil : When the time between the pulses is measured the period for one rotation
can be found, and the frequency calculated. This technique often requires some signal
conditioning circuitry. Another common technique uses a simple permanent magnet DC generator (note:
you can also use a small DC motor). The generator is hooked to the rotating shaft. The
rotation of a shaft will induce a voltage proportional to the angular velocity. This technique
will introduce some drag into the system, and is used where efficiency is not an
issue.
Both of these techniques are common, and inexpensive.
Linear position ;
Rotational potentiometers were discussed before, but potentiometers are also
available in linear/sliding form. These are capable of measuring linear displacement over
long distances.
Linear Variable Differential Transformers (LVDT)
Linear Variable Differential Transformers (LVDTs) measure linear displacements
over a limited range. The basic device is shown in Figure 14.8. It consists of outer coils
with an inner moving magnetic core. High frequency alternating current (AC) is applied to
the center coil. This generates a magnetic field that induces a current in the two outside
coils. The core will pull the magnetic field towards it, so in the figure more current will be
induced in the left hand coil. The outside coils are wound in opposite directions so that
when the core is in the center the induced currents cancel, and the signal out is zero
(0Vac). The magnitude of the signal out voltage on either line indicates the position of the
core. Near the center of motion the change in voltage is proportional to the displacement.
But, further from the center the relationship becomes nonlinear.
Moire Fringes
High precision linear displacement measurements can be made with Moire
Fringes : Both of the strips are transparent (or reflective), with
black lines at measured intervals. The spacing of the lines determines the accuracy of the
position measurements. The stationary strip is offset at an angle so that the strips interfere
to give irregular patterns. As the moving strip travels by a stationary strip the patterns will
move up, or down, depending upon the speed and direction of motion.
These are used in high precision applications over long distances, often meters.
They can be purchased from a number of suppliers, but the cost will be high. Typical
applications include Coordinate Measuring Machines (CMMs).
Accelerometers
Accelerometers measure acceleration using a mass suspended on a force sensor :
When the sensor accelerates, the inertial resistance of the mass
will cause the force sensor to deflect. By measuring the deflection the acceleration can be
determined. In this case the mass is cantilevered on the force sensor. A base and housing
enclose the sensor. A small mounting stud (a threaded shaft) is used to mount the accelerometer.
Accelerometers are dynamic sensors, typically used for measuring vibrations between 10Hz to 10KHz. Temperature variations will affect the accuracy of the sensors.
Standard accelerometers can be linear up to 100,000 m/s**2: high shock designs can be
used up to 1,000,000 m/s**2. There is often a trade-off between a wide frequency range
and device sensitivity (note: higher sensitivity requires a larger mass).
The force sensor is often a small piece of piezoelectric material (discussed later in
this chapter). The piezoelectic material can be used to measure the force in shear or compression.
Piezoelectric based accelerometers typically have parameters such as,
-100 to 250°C operating range
1mV/g to 30V/g sensitivity
operate well below one forth of the natural frequency
The accelerometer is mounted on the vibration source : The accelerometer is electrically isolated from the vibration source so that the sensor may
be grounded at the amplifier (to reduce electrical noise). Cables are fixed to the surface of
the vibration source, close to the accelerometer, and are fixed to the surface as often as
possible to prevent noise from the cable striking the surface. Background vibrations can be
detected by attaching control electrodes to non-vibrating surfaces. Each accelerometer is
different, but some general application guidelines are;
• The control vibrations should be less than 1/3 of the signal for the error to be less
than 12%).
• Mass of the accelerometers should be less than a tenth of the measurement mass.
• These devices can be calibrated with shakers, for example a 1g shaker will hit a
peak velocity of 9.81 m/s**2.
Accelerometers are commonly used for control systems that adjust speeds to
reduce vibration and noise. Computer Controlled Milling machines now use these sensors
to actively eliminate chatter, and detect tool failure. The signal from accelerometers can be integrated to find velocity and acceleration.
Forces and Moments
Strain Gages
Strain gages measure strain in materials using the change in resistance of a wire.
The wire is glued to the surface of a part, so that it undergoes the same strain as the part (at
the mount point).
Piezoelectric
When a crystal undergoes strain it displaces a small amount of charge. In other
words, when the distance between atoms in the crystal lattice changes some electrons are
forced out or drawn in. This also changes the capacitance of the crystal.
Liquids and Gases
There are a number of factors to be considered when examining liquids and gasses.
• Flow velocity
• Density
• Viscosity
• Pressure
There are a number of differences factors to be considered when dealing with fluids
and gases. Normally a fluid is considered incompressible, while a gas normally follows
the ideal gas law. Also, given sufficiently high enough temperatures, or low enough
pressures a fluid can be come a liquid. When flowing, the flow may be smooth, or laminar. In case of high flow rates or
unrestricted flow, turbulence may result. The Reynold’s number is used to determine the
transition to turbulence.
Pressure
The different two mechanisms for pressure measurement. The
Bourdon tube uses a circular pressure tube. When the pressure inside is higher than the
surrounding air pressure (14.7psi approx.) the tube will straighten. A position sensor, connected
to the end of the tube, will be elongated when the pressure increases.
Venturi Valves
When a flowing fluid or gas passes through a narrow pipe section (neck) the pressure
drops. If there is no flow the pressure before and after the neck will be the same. The
faster the fluid flow, the greater the pressure difference before and after the neck.
Coriolis Flow Meter
Fluid passes through thin tubes, causing them to vibrate. As the fluid approaches
the point of maximum vibration it accelerates.
Magnetic Flow Meter
A magnetic sensor applies a magnetic field perpendicular to the flow of a conductive
fluid. As the fluid moves, the electrons in the fluid experience an electromotive force.
Ultrasonic Flow Meter
A transmitter emits a high frequency sound at point on a tube. The signal must then
pass through the fluid to a detector where it is picked up. If the fluid is flowing in the same
direction as the sound it will arrive sooner. If the sound is against the flow it will take
longer to arrive. In a transit time flow meter two sounds are used, one traveling forward,
and the other in the opposite direction. The difference in travel time for the sounds is used
to determine the flow velocity.
A doppler flowmeter bounces a soundwave off particle in a flow. If the particle is
moving away from the emitter and detector pair, then the detected frequency will be lowered,
if it is moving towards them the frequency will be higher.
The transmitter and receiver have a minimal impact on the fluid flow, and therefore
don’t result in pressure drops.
Vortex Flow Meter
Fluid flowing past a large (typically flat) obstacle will shed vortices. The frequency
of the vortices will be proportional to the flow rate. Measuring the frequency
allows an estimate of the flow rate. These sensors tend be low cost and are popular for low
accuracy applications.
Positive Displacement Meters
In some cases more precise readings of flow rates and volumes may be required.
These can be obtained by using a positive displacement meter. In effect these meters are
like pumps run in reverse. As the fluid is pushed through the meter it produces a measurable
output, normally on a rotating shaft.
Temperature
Temperature measurements are very common with control systems. The temperature
ranges are normally described with the following classifications.
very low temperatures <-60 deg C - e.g. superconductors in MRI units
low temperature measurement -60 to 0 deg C - e.g. freezer controls
fine temperature measurements 0 to 100 deg C - e.g. environmental controls
high temperature measurements <3000 deg F - e.g. metal refining/processing
OBJECTIVES AND CONSTRAINTS
• Objectives are those things we want to minimize, or maximize.
- money
- time
- mass
- volume
- power consumption
- some combination of factors
SEARCHING FOR THE OPTIMUM
• Local Search Space
• A topographical map shows the relationship between search parameters and cost
values.
OPTIMIZATION ALGORITHMS
• The search algorithms change system parameters and try to lower system parameters.
• The main question is how to change the system parameters to minimize the system
value.
Training a Neural Network for Inverse Kinematics
Neural Network solutions have the benefit of having faster processing times since information is processed
in parallel. The solutions may be adaptive and still be implemented in hardware by using specialized electronics. Neural
systems can generalize to approximate solutions from small training sets. Neural systems are fault tolerant and
robust. The network will not fail if a few neurons are damaged, and the solutions may still retain accuracy. When
implementing a neural network approach, complex computers are not essential and robot controllers need not be specific to any one manipulator.
EMBEDDED CONTROL SYSTEM
INTRODUCTION
• Elements of embedded systems (with program examples of each)
NOTE: emphasize a top-down program structure with subroutines for each
one.
logical IO - digital inputs and outputs
analog outputs - immediate
analog inputs - delayed in (show use of nops and loop to wait), use potentiometer
timers including PWM to control transisor/h-bridge for motor control,
show sound generation also.
counters including encoder decoding and tachometer decoding
serial IO
other peripherals such as displays, sounds, etc.
• Control system fundamentals
a simple PID feedback loop using nops and time calcs to ensure time
a multiple step process that waits for an input and does a task with the PID
loop. Show an executive subroutine and calls to
dealing with events
event types; asynchronous, delayed
polling
interrupts
• Concurrent processes
single thread vs concurrent processing
how to implement a single control thread
how to create multiple processes
real-time
the need for multiple processes
non-time critical
time critical; regular updates and minimum time between runs
priority levels
hard vs. soft
• Structured Design
General systems design topics
show the general structure of a program with an executive routine
that calls task routines.
show a program that mixes an asynchronous GUI mixed with a
realtime routine
Modal System design
show the use of global mode bits to track the mode of the system
show how the mode bits changes the flow of execution in the executive
routine.
Flowcharts
map flowchart structures to program structure
using a register value to track the location in the flowchart
State Diagrams
show the use of state diagrams to model a process and then how the
program is written for it.
Failure Analysis
show basic probability theory
show parallel vs serial failures
show failure estimation using theory for single and chained failure
modes
show the methods for categorizing failures as a hazard, danger, etc.
• Communication
Receiving and sending strings
String Handling
Parsing strings
Composing strings
Command and response structures
Error Checking
Non byte oriented data
Networked structured, ie destination address header
A full feedback control system
• Other topics
Keyboard multiplexing
output refreshing, LEDs
VIII . Wireless and personal communications systems as a concept of RADAR for point LASER Tracking
THE TERM WIRELESS WAS COINED IN THE LATE NINETEENTH CENTURY WHEN inventors toyed with the idea of sending and receiving telegraph messages using electromagnetic fields rather than electric currents. In the early twentieth century, the technology became known as radio; video and data broadcasting and communications were added in the middle of the century and the general term electromagnetic communications emerged. The word wireless was relegated to history. In the late 1980s, the term found new life. Today it refers to communications, networking, control devices, and security systems in which signals travel without direct electrical connections.
Cellular communications Radio transceivers can be used as telephones in a specialized communications system called cellular. Originally, the cellular communications network was patchy and unreliable, and was used mainly by traveling business people. Nowadays, cellular telephone units are so common that many people regard them as necessities.
How cellular systems work A cellular telephone set, or cell phone, looks and functions like a cross between a cordless telephone receiver and a walkie-talkie. The unit contains a radio transmitter and receiver combination called a transceiver. Transmission and reception take place on different frequencies, so you can talk and listen at the same time. This capability, which allows you to hear the other person interrupt you if he or she chooses, is known as full duplex.
In an ideal cellular network, all the transceivers are always within range of at least one repeater. The repeaters pick up the transmissions from the portable units and retransmit the signals to the telephone network and to other portable units. The region of coverage for any repeater (also known as a base station) is called a cell. When a cell phone is in motion, say in a car or on a boat, the set goes from cell to cell in the network. This situation is shown in Fig. 32-1. The curved line is the path of the vehicle. Base stations (dots) transfer access to the cell phone. This is called handoff. Solid lines show the limits of the transmission/reception range for each base station. All the base stations are connected to the regional telephone system. This makes it possible for the user of the portable unit to place calls to, or receive calls from, anyone else in the system, whether those other subscribers have cell phones or regular phones.
Older cellular systems occasionally suffer from call loss or breakup when signals are handed off from one repeater to another. This problem has been largely overcome by a technology called code-division multiple access (CDMA). In CDMA, the repeater coverage zones overlap significantly, but signals do not interfere with each other because every phone set is assigned a unique signal code. Rather than abruptly switching from one base-station zone to the next, the signal goes through a region in which it is actually sent through more than one base station at a time. This make-before-break scheme gets rid of one of the most annoying problems inherent in cellular communications. To use a cellular network, you must purchase or rent a transceiver and pay a monthly fee. The fees vary, depending on the location and the amount of time per month you use the service. When using such a system, it is important to keep in mind that your conversations are not necessarily private. It is easier for unauthorized people to eavesdrop on wireless communications than to intercept wire or cable communications.
Cell phones and computers A personal computer (PC) can be hooked up to the telephone lines for use with online networks such as the Internet. For some people, getting on the Internet is the most important justification for buying a computer. You can connect a laptop or notebook computer to a cell phone with a portable modemthat converts incoming computer data from analog to digital and also converts outgoing data from digital to analog.
Most commercial aircraft have telephones at each row of seats, complete with jacks into which you can plug a modem. If you plan to get on-line from an aircraft, you must use the phones provided by the airline, not your own cell phone, because radio transceivers can cause interference to flight instruments. You must also observe the airline’s restrictions concerning the operation of electronic equipment while in flight. If you aren’t sure what these regulations are, ask one of the flight attendants.
Satellite systems
A satellite system is, in a certain sense, a gigantic cellular network. The repeaters, rather than being in fixed locations, are constantly moving. The zones of coverage
are much larger in a satellite network than in a cellular network, and they change in size and shape if the satellite moves relative to the earth’s surface.
Geostationary-orbit satellites For any satellite in a circular orbit around the earth, the revolution period gets longer as the altitude increases. At an altitude of about 22,300 miles, a satellite in a circular orbit takes precisely one day to complete each revolution. If a satellite is placed in such an orbit over the equator, and if it revolves in the same direction as the earth rotates, it is called a geostationary-orbit (GEO) satellite or simply a geostationary satellite. From the viewpoint of someone on the earth, a GEO satellite stays in the same spot in the sky all the time. One GEO satellite can cover about 40 percent of the earth’s surface. A satellite over Ecuador, for example, can link most cities in North America and South America. Three satellites in geostationary orbits spaced 120 degrees apart (one-third of a circle) provide coverage over the entire civilized world. Geostationary satellites are used in television (TV) broadcasting, telephone and data communication, for gathering weather and environmental data, and for radiolocation. In GEO-satellite networks, earth-based stations can communicate via a single “bird” only when the stations are both on a line of sight with the satellite. If two stations are nearly on opposite sides of the planet, say in Australia and Wisconsin, they must operate through two satellites to obtain a link (Fig. 32-3). In this situation, signals are relayed between the two satellites, as well as between either satellite and its respective earth-based station. The main problem with two-way GEO-satellite communication is the fact that the signal path is long: at least 22,300 miles up to the satellite, and at least 22,300 miles back down to the earth. If two satellites are used in the circuit, the path is substantially
longer. This doesn’t cause problems in television broadcasting or in one-way data transfers, but it slows things down when computers are linked with the intention of combining their processing power. It is also noticeable in telephone conversations.
Low-earth-orbit satellites The earliest communications satellites orbited only a few hundred miles above the earth. They were low-earth-orbit (LEO) satellites. Because of their low orbits, LEO satellites took only about 90 minutes to complete one revolution. This made communication spotty and inconvenient, because a satellite was in range of any given ground station for only a few minutes at a time. Because of this, GEO satellites became predominant. However, GEO satellites have certain limitations. A geostationary orbit requires constant adjustment, because a tiny change in altitude will cause the satellite to get out of sync with the earth’s rotation. Geostationary satellites are expensive to launch and maintain. When communicating through them, there is always a delay because of the path length. It takes high transmitter power, and a sophisticated, precisely aimed antenna, to communicate reliably. These problems with GEO satellites have brought about a revival of the LEO scheme. Instead of one single satellite, the new concept is to have a large fleet of them. Imagine dozens of LEO satellites in orbits such that, for any point on the earth, there is always at least one satellite in range. Further, suppose that the satellites can relay messages throughout the fleet. Then any two points on the surface can always make, and maintain, contact through the satellites. A LEO system employs satellites in orbits strategically spaced around the globe. The satellites are placed in polar orbits (routes that pass over or near the earth’s geographic poles) because such orbits optimize the coverage of the system. A LEO satellite wireless communications link is easier to access and use than a GEO satellite link. A small, simple antenna will suffice, and it doesn’t have to be aimed in any particular direction. The transmitter can reach the network using only a few watts of power. The propagation delay is much shorter than is the case with a geostationary link, usually much less than 0.1 second.
Medium-earth-orbit satellites Some satellites revolve in orbits higher than those normally considered low-earth, but at altitudes lower than the geostationary level of 22,300 miles. These intermediate
“birds” are called medium-earth-orbit (MEO) satellites. A MEO satellite takes several hours to complete each orbit. MEO satellites operate in fleets, in a manner similar to the way LEO satellites are deployed. Because the average MEO altitude is higher than the average LEO altitude, each “bird” can cover a larger region on the surface at any given time. A fleet of MEO satellites can be smaller than a comparable fleet of LEO satellites, and still provide continuous, worldwide communications. The orbits of GEO satellites are essentially perfect circles, and most LEO satellites orbit in near-perfect circles. But MEO satellites often have elongated, or elliptical, orbits. The point of lowest altitude is called perigee; the point of greatest altitude is called apogee. The apogee can be, and often is, much greater than the perigee. Such a satellite orbits at a speed that depends on its altitude. The lower the altitude, the faster the satellite moves. A satellite with an elliptical orbit crosses the sky rapidly when it is near perigee, and slowly when it is near apogee; it is easiest to use when its apogee is high above the horizon, because then it stays in the visible sky for a long time. Every time a MEO satellite completes one orbit, the earth rotates beneath it. The rotation of the earth need not, and usually does not, correspond to the orbital period of the satellite. Therefore, successive apogees for a MEO satellite occur over different points on the earth’s surface. This makes the tracking of individual satellites a complicated business, requiring computers programmed with accurate orbital data. For a MEO system to be effective in providing worldwide coverage without localized periodic blackouts, the orbits must be diverse, yet coordinated in a precise and predictable way. In addition, there must be enough satellites so that each point on the earth is always on a line of sight with one or more satellites, and preferably, there should be at least one “bird” in sight near apogee at all times.
The Global Positioning System
The Global Positioning System (GPS) is a network of satellites that operates on a worldwide basis. This system allows a user to determine exact latitude, longitude, and (if applicable) altitude. All GPS satellites transmit signals in the microwave part of the radio spectrum, where the wavelengths are a few centimeters. The signals are modulated with special timing and identification codes. A GPS receiver allows its user to find his or her position by measuring the distances to four different satellites. This is done by precisely timing the signals as they travel between the satellites and the receiver. The receiver uses a computer to process the information received from the satellites. From this information, it can give the user an indication to within a few feet (for government and industrial subscribers) or a few hundred feet (for civilians). An increasing number of automobiles, trucks, and pleasure boats have GPS receivers installed. If you are driving your car in a remote area and get stranded, say in a blizzard, you might use the GPS to locate your position. Using a cell phone, you could call for help and inform authorities of your location. Someday, perhaps every motor vehicle and boat will be equipped with GPS and wireless communications equipment.
Acoustic transducers
An acoustic transducer is an electronic component that converts sound waves into some other form of energy, or vice versa. The other form of energy is usually an alternating-current (ac) electrical signal. The waveforms of the acoustical and electrical signals are identical, or nearly so. Acoustic transducers are designed for various frequency ranges. The human hearing spectrum extends from about 20 Hz to 20 kHz. But acoustic energy can have frequencies lower than 20 Hz or higher than 20 kHz. Energy at frequencies below 20 Hz is called infrasound; if the frequency is above 20 kHz, it is known as ultrasound. In acoustic wireless devices, ultrasound is generally used, because the wavelength is short and the necessary transducers can be small. Also, ultrasound cannot be heard, and therefore it will not distract or annoy people.
currents when it is subjected to mechanical stress. Therefore, an ac voltage develops between the two metal plates, with a waveform similar to that of the acoustic waves. If an ac signal is applied to the plates, it causes the crystal to vibrate in sync with the current. The result is that the metal plates vibrate also, producing an acoustic disturbance in the air. The piezoelectric transducer can thus act either as an acoustic pickup or an acoustic emitter. Piezoelectric transducers are common in ultrasonic applications, such as intrusion detection systems.
The most well-known type of acoustic transducer has a coil surrounding a permanent magnet or electromagnet. A diaphragm or cone is attached to either the coil or the magnet. When the diaphragm vibrates as a result of acoustic waves striking it, ac is produced in the coil. Conversely, if ac is applied to the coil, it produces electromagnetic force that causes the diaphragm to vibrate. This device is called a dynamic transducer. Most microphones, headphones, and loudspeakers are of this type. Acoustic transducers are used in security systems. They are also used in robotics to help mobile machines navigate in their surroundings. Acoustic transducers are employed in depth-finding apparatus commonly found on boats. Radio-frequency transducers The term radio-frequency (RF) transducer is a fancy name for an antenna. Antennas are so common that you probably don’t think about them very often. Your car radio has one. Your portable headphone radio, which you might use while jogging on a track (but never in traffic), employs one. Cellular and cordless telephones, portable television receivers, and handheld radio transceivers use antennas. Hundreds of books have been written on the subject. There are two basic types of RF transducer: the receiving antennaand the transmitting antenna.A receiving antenna converts electromagnetic (EM) fields, in the RF
range from about 9 kHz to several hundred gigahertz, into ac signals that are amplified by the receiving apparatus. A transmitting antenna converts powerful alternating currents into EM fields, which propagate through space. There are a few significant differences between receiving antennas and transmitting antennas designed for a specific radio frequency. The efficiency of an antenna is important in transmitting applications, but not so important in reception. Efficiency is the percentage of the power going into a transducer that is converted into the desired form. If the input power to a transducer is Pin watts and the output power is Pout watts, the efficiency in percent, Eff%, can be found using the following equation:
Eff% 100 Pout/Pin
Infrared transducers Many wireless devices transmit and receive energy at infrared (IR) wavelengths, rather than at radio wavelengths. Infrared energy has a frequency higher than that of radio waves, but lower than that of visible light. Infrared is sometimes called heat radiation, but this is a misnomer. Some wireless devices transmit and receive their signals in the visible-light range, although these are encountered much less often than IR devices. The most common IR transmitting transducer is the infrared-emitting diode (IRED). You learned about this type of diode in chapter 20. A fluctuating direct current is applied to the IRED. The current causes the device to emit IR rays; the fluctuations in the current constitute the modulation, and produce rapid variations in the intensity
of the rays emitted by the semiconductor junction. The modulation contains information, such as which channel your television set should seek, or whether the volume is to be raised or lowered. Infrared energy is not visible, but at some wavelengths it can be focused by ordinary optical lenses and reflected by ordinary optical mirrors. This makes it possible to collimate IR rays (make them essentially parallel) so they can be transmitted for distances up to several hundred feet. Infrared receiving transducers resemble photodiodes or photovoltaic cells, which were also discussed in chapter 20. The only real difference is that the diodes are maximally sensitive in the IR, rather than in the visible, part of the electromagnetic spectrum. The fluctuating IR energy from the transmitter strikes the P/N junction of the receiving diode. If the receiving device is a photodiode, a current is applied to it, and this current varies rapidly in accordance with the signal waveform on the IR beam from the transmitter. If the receiving device is a photovoltaic cell, it produces the fluctuating current all by itself, without the need for an external power supply. In either case, the current fluctuations are weak, and must be amplified before they are delivered to whatever equipment (television set, garage door, oven, security system, etc.) is controlled by the wireless system. Infrared wireless devices work best on a line of sight, that is, when the transmitting and receiving transducers are located so the rays can travel without encountering any obstructions. You have probably noticed this when using television remote control boxes, most of which work at IR wavelengths. Sometimes enough energy will bounce off the walls or ceiling of a room to let you change the channel when the remote box is not on a direct line of sight with the television set. But the best range is obtained by making sure you and the television set can “see” each other. You cannot put an IR control box in your pants pocket and expect it to work. Radio and IR control boxes are often mistaken for one another because they look alike to the casual observer. Wireless local area networks A local area network (LAN) is a group of computers linked together within a building, campus, or other small region. The interconnections in early LANs were made with wire cables, but increasingly, radio links are being used. A wireless LAN offers flexibility because the computer users can move around without having to bother with plugging and unplugging cables. This arrangement is ideal when notebook computers (also known as laptops) are used. The way in which a LAN is arranged is called the LAN topology.There are two major topologies: the client-server wireless LAN and the peer-to-peer wireless LAN. In a client-server wireless LAN (Fig. 32-6), there is one large, powerful, central computer called a file server, to which all the smaller personal computers (labeled PC) are linked. The file server has enormous computing power, high speed, and large storage capacity, and can contain all the data for every user. End users do not communicate directly. All the data must pass through the file server. In a peer-to-peer LAN (Fig. 32-7), all of the computers in the network are PCs with more or less equal computing power, speed, and storage capacity. Each user generally maintains his or her own data. Subscribers can, and almost always do, communicate .
directly without the data having to pass through any intermediary. This offers greater privacy and individuality than the client-server topology, but it is slower when a large number of users need to share data. In the illustrations, only three PCs are shown in the networks. But any LAN can have as few as two, or as many as several dozen, PC workstations. Client-server LANs are favored by large institutions. Small businesses and schools, or departments within a larger corporation or university, prefer to use peer-to-peer LANs, mainly because they are cheaper and easier to maintain. Wireless security systems Wireless technology lends itself to certain security applications, especially those involving mobile vehicles such as cars, boats, and trucks. Also, a wireless link can alert you to a fire or intrusion at your home or business, when you are not physically present at the location. One well-known wireless security system for cars employs a device that transmits a radio signal when the vehicle is being improperly operated. The system circuits and antenna are concealed, although there might be a warning sticker on the
car. If a potential thief knows your vehicle has a wireless security system, he or she will probably not want to spend a lot of time snooping around to find and disable the system. If someone manages to steal your car and it has a wireless security system installed, and if you’re lucky enough to find out about the theft within a short time, tell the police about the security system. The police have a wireless transmitter that sends out a signal that contains the vehicle identification number (VIN) for your car. This signal is received by the equipment in your car, which starts up its own transmitter. Using radiolocation equipment, the police can pinpoint the position of your car on a map. From there, mobile direction-finding radio receivers can be used to reach the car. In some cases the police have caught thieves while they were actually driving stolen cars. A home or business wireless security system operates like a paging device or beeper. If something happens that triggers the security system, a radio signal is transmitted that sets off a small radio receiver you carry. Such a system will ideally telephone the police and/or fire department as well. If you happen to be reasonably near your home or business, you can drive to the site. Hobby radio In most countries of the world, people can obtain government-issued licenses to send and receive messages via radio for nonprofessional purposes. In America, this hobby is called amateur radio or ham radio. If you want only to listen to communications and broadcasting, and not to transmit signals, you do not need a license in the United States (although you might need one in certain other countries).
Who uses amateur radio? Anyone can use ham radio. Amateur radio operators, often called radio hams, can communicate using any of numerous modes, including speech, Morse code, television, and radioteletype (RTTY). This last mode, RTTY, can be done in real time, or by posting messages in a manner similar to the way computer users exchange information by electronic mail (e-mail). Radio hams have set up their own radio networks. Some of these networks have Internet gateways. This is known as packet radio. Some radio hams chat about anything they can think of (except business matters, which are illegal to discuss via ham radio). Others like to practice emergency-communications skills, so they can be of public service during crises such as hurricanes, earthquakes, or floods. Still others like to go out into the wilderness and talk to people thousands of miles away while sitting out under the stars. Amateur radio operators communicate from cars, boats, aircraft, and bicycles; this is called mobile operation. When transceivers are used while walking or hiking, it is known as portable or handheld operation.
computers. The station can be equipped for on-line telephone (landline) services. The PC can control the antennas for the station and can keep a log of all stations that have been contacted. Some transceivers can be operated by computer, either locally or by remote control over the radio or landline. A good way to learn about ham radio is to contact the headquarters of the American Radio Relay League, 225 Main Street, Newington, CT 06111. Their Web site is at http://www.arrl.org.
Computers and the Internet
DURING THE 1980S, PERSONAL COMPUTING BOOMED INTO A HOBBY. BY THE mid-1990s, these machines, which had been esoteric to most people only a generation before, were common electronic appliances in households, businesses, and government agencies at all levels. Computers are used for communications, word processing, data processing, arithmetic and mathematical calculations, drawing, photo processing, music composition, radio location, radio navigation, information searches, robot control, and many other purposes. There are two major “lines” of personal and small-business computers: IBM (International Business Machines) -compatible and Macintosh (often called “the Mac”). There are a few other, less-well-known systems. Regardless of the “line,” however, all computers have similar components. Figure 33-1 is a block diagram showing the major parts of a typical small computer system, such as the kind you might buy for personal or small-business use. The microprocessor and CPU The microprocessor is the integrated circuit (IC), or chip, that forms the core of your computer’s “brain.” It coordinates all the action and does all the calculations. It is located on the motherboard, or main circuit board, of the main unit. This board is sometimes called the logic board.
Basic components The microprocessor, together with various other circuits, comprise the central processing unit (CPU) of a computer. Auxiliary circuits can be integrated onto the same chip as the microprocessor, but they are often separate. The external chips contain memory and programming instructions. You might think of the microprocessor as the computer’s conscious mind, which directs the behavior of the machine by deliberate control. The CPU, dominated by the microprocessor, represents the PC’s entire mind, conscious and subconscious. All the ancillary circuits, in conjunction with the CPU, create the computer’s central nervous system. Peripherals such as printers, disk drives, mice, speech recognition/synthesis apparatus, modems, and monitors are the hands, ears, eyes, and mouth of the machine. (There is, as of this writing, no common computer analog for the human nose. But it’s probably only a matter of time.) In advanced computer systems there might be robots, vision systems, various home appliances, surveillance apparatus, medical devices, and other exotic equipment under the control of the CPU. Microprocessors get more powerful every year. Physically, this translates to an increasing number of digital switching transistors per chip. The Intel 486, a primitive chip by today’s standards, had more than 1,000,000 transistors. The number of digital switches that can be fabricated onto a semiconductor chip of a particular size is limited only by the structure of matter. It’s possible that someday an elementary logic unit, called a binary digit or bit, will be represented by the presence or absence of a single electron in an atom. Some researchers have even discussed the possibility that a single electron might represent more than one data bit at a time. Of course, factors that we don’t yet know about will probably enter into this picture. Alternatives to digital technology, such as analog computers or neural networks, might produce new developments, creating machines with power and speed that we can only dream about today. There is considerable disagreement about this, however. More than a few scientists think that the digital modus operandi has won the cyber-supremacy battle for all time.
Bytes, kilobytes, megabytes, and gigabytes Abyteis a unit of digital data, consisting of a string of eight bits. One byte constitutes roughly the same amount of data as one character, such as a letter, numeral, punctuation mark, space, or line-feed/return command. Today’s computers work with files that are very large in terms of bytes. Therefore, kilobytes (units of 210 1024 bytes), megabytes (units of 220 1,048,576 bytes), and gigabytes(units of 230 1,073,741,824 bytes) are commonly mentioned by people talking about computers. The abbreviations for these units are KB, MB, and GB, respectively. Alternatively you might see them abbreviated as K, M, and G. As computer technology advances during the new century, you’ll be hearing more and more about a unit of data called a terabyte(TB or T). This is equivalent to 240 bytes, or 1,048,576 MB. And the day might come when we commonly use the terms petabyte (PB or P), which refers to 250 bytes or 1,048,576 GB, and even exabyte(EB or E), which refers to 260 bytes of 1,048,576 TB. Does that sound incredible? If so, think about the fact that even a computer with storage or memory capacities in the exabyte range cannot begin to approach the sophistication and subtlety of the human mind. But nevertheless, a machine juggling a few exabytes of data might have a fascinating, if perhaps alien, sort of intelligence. Personal-computer memory is usually specified in megabytes or gigabytes. The same holds true for removable data storage media such as diskettes.Thehard drivein a computer generally has capacity measured in gigabytes, although a few get into the terabyte range. Older computers might have hard-drive capacities quoted as a few hundred megabytes or less. The hard drive A hard drive, also known as a hard disk, is a common form of mass storage for computer data. The drive consists of several disks, called platters, arranged in a stack. They are made from aluminum or other rigid material, coated with a ferromagnetic substance similar to that used in audio or video tape. The platters are spaced a fraction of an inch apart. Each has two sides (top and bottom) and two read/write heads(one for the top and one for the bottom). The assembly is enclosed in a sealed cabinet. Figure 33-2A is an edgewise, cutaway view of the platters and heads in a typical hard drive.
Drive action When the computer is switched off, the hard drive mechanism locks the heads in a position away from the platters. This prevents damage to the heads and platters if the computer is moved. When the computer is powered up, the platters spin at several thousand revolutions per minute (rpm). The heads hover a few millionths of an inch above and below the platter surfaces. When you type a command or click on an icon telling the computer to read or write data, the hard drive mechanism goes through a series of rapid, complex, and precise movements. The head must be positioned over the particular spot on the platter where
the data is located or is to be written. Then the head must stabilize its position and generate or detect the magnetic fields. All this takes place in a small fraction of a second.
Data arrangement and capacity The data on a hard drive is arranged in circular tracks. This is not quite like the spiral groove on an old-fashioned phonograph disk. While that groove is one long path, the tracks on a platter are individual circles. There are hundreds or even thousands of tracks per radial inch of the platter surface. Each circular track is broken into a
number of arcs called sectors. A cylinder is the set of equal-radius tracks on all the platters in the drive. Tracks and sectors are set up on the hard drive during the initial formatting process. There are also data units called clusters. These are units consisting of one to several sectors, depending on the arrangement of data on the platters. Figure 33-2B is a face-on view of a single hard-disk platter, showing a track and one of its constituent sectors. The average new computer hard-drive data storage capacity roughly doubles every year, and thus increases by about three orders of magnitude per decade. At the end of the year 2000, during the holiday computer-buying season, a new desktop machine had between 10 and 100 GB of hard-drive capacity. By the end of the year 2010, if trends continue, these figures will be approximately 1000 times greater—a range of 10 to 100 TB. Do petabyte and exabyte machines mentioned a few paragraphs ago seem out of this world, impossible, or ridiculous? Extrapolate. Chances are good that you will live to see them. When you buy a computer, whether it is a desktop, notebook (also called laptop), or portable (also called handheld) unit, it will have a hard drive built in. The drive comes installed and formatted. Most new computers are sold with several commonly used programs preinstalled on the hard drive. Some computer users prefer to buy new computers with only the operating system, by means of which the programs run, installed; this frees up hard-drive space and gives the user control over which programs to install (or not to install). Other forms of mass storage There are several types of mass storage (besides the hard drive) in which data can be kept in large quantities. Computer experts categorize mass storage in two ways: access time and cost per megabyte. In general, the less the access time (that is, the faster the storage medium), the greater the cost per megabyte. The fastest mass storage media usually have the lowest capacity.
Flash memory Flash memory is an all-electronic form of storage that is useful especially in highlevel graphics, big-business applications, and scientific work. The capacity is comparable to that of a small hard drive, but there are no moving parts. Because there are no mechanical components, flash memory is faster than any other mass-storage scheme. PC cards (also called PCMCIA cards) are credit-card-sized, removable components, some of which are designed to serve as removable flash memory.
Disk media Magnetic diskettes, also called (imprecisely) “floppies,” are 3.5 inches in diameter and enclosed in a rigid, square case about 4 millimeters thick. They can be interchanged in seconds, so there is no limit to how much data you can put on them. But their capacity, individually, is limited. A full-wall bookcase of diskettes could hold more work than you’d create in your lifetime. Zip and Jaz disks (trademarks of Iomega Corporation) are slightly larger than 3.5inch diskettes in physical dimension, but vastly larger in storage capacity. The original
Zip disks can hold about 100 MB of data; newer ones can hold 250 MB. Jaz disks hold about 1 GB. There are several variants on the Zip/Jaz theme, produced by various manufacturers. All these disk types require special drives. Some new computers include built-in Zip drives. A popular mass-storage medium is compact-disk, read-only memory(CD-ROM). You can buy CD-ROMs for various applications. They are commonly used for commercial software and also to store reference materials such as dictionaries and telephone directories. The main asset of CD-ROM is its fairly large capacity and its long shelf life. The main drawback is that the medium cannot be erased and overwritten, unless you are willing to spend the money for a compact-disk, recordable (CD-R) drive.
Tape media The earliest computers used magnetic tape to store data. This is still done in some systems. You can get a tape drive for making an emergency backup of the data on your hard drive, or for archiving data you rarely need to use. Magnetic tape has very high storage capacity. There are microcassettes that can hold more than 1 GB of data; standard cassettes can hold many gigabytes. But tapes are extremely slow because, unlike their disk-shaped counterparts, they are a serial-access storage medium. This means that the data bits are written in a string, one after another, along the entire length of the tape. The drive might have to mechanically rewind or fast-forward through a football field’s length of tape to get to a particular data bit, whereas on a disk medium, the read/write head never has to travel further than the diameter of the disk to reach a given data bit. Random-access memory In a computer, the term random-access memory (RAM) refers to integrated circuits (ICs) that store working data. The amount, and speed, of memory is a crucial factor in determining what a computer can and cannot do.
Data flow Figure 33-3 shows how data moves between a hard drive or diskette and the memory, controlled by the CPU. When you open a file on your hard drive or on a diskette, the data goes immediately into the memory. The CPU, under direction of the microprocessor, manipulates the data in the memory as you work on the file. Thus, the data in memory changes from moment to moment. When you hit a key to add a character, or drag the mouse to draw a line that shows up on your display, that character or line goes into memory at the same time. If you hit the backspace key to delete a character, or drag the mouse to erase a line on the screen, it disappears from the memory. During this time the original file on the disk stays as it was before you accessed it. No change is made to the disk data until you specifically instruct the computer to overwrite the data on the disk. When you’re done working on a file, you tell the microprocessor to close it. Then the data leaves memory and goes back to the hard drive or diskette from which it came, or to some other place, as you might direct. If you tell the computer to overwrite the file on the disk from which it came, many programs send the new data (containing the changes you have made) to unused space on the disk; the old data (as it was before you opened the file) stays in its old location. This is a safeguard, in case you decide to undo the changes you made. All the data passing between the disks and the memory, and between the memory and the CPU, is in machine language. This consists of binary digits (bits) 0 and 1. But the data passing between you and the CPU is in plain English (or whatever other language you prefer), or in some high-level programming language, having been translated by the machine into a form you can understand.
Memory capacity The maximum number of bytes of data that can be stored in a computer’s memory is known as the memory capacity. The main factor that determines memory capacity is the number of transistors that can be fabricated onto a single memory IC, or “chip.” Other factors, such as microprocessor speed, have a practical effect on the usable memory capacity. A gigantic memory will not be of much use if the microprocessor is slow. Nor will a fast microprocessor be of practical value if the memory capacity is too small for applications that demand high speed. The amount of memory you need depends on the applications you intend to run on your computer. Most software packages will tell you how much memory you need. They’ll often quote two specifications: a minimum memory requirement and a figure for optimum performance (approximately twice the minimum requirement). If possible, you should equip your computer with enough memory for optimum performance. This year’s optimum machine is next year’s minimal one when it comes to popular software. If your computer lacks the memory to run a given application, you can usually add more. But this can only be done up to a certain point. Eventually, your microprocessor will no longer be able to run contemporary software at reasonable speed, no matter how much memory you have. When buying a new computer, it’s not a bad idea to err on the side of “too much” memory, rather than risk running short. How much memory do you think your machine will require to run two or three of your favorite applications at the same time? Double or triple it, and you will come close to the amount you are likely to need for the next two or three years, until you are overcome by the urge to buy a new computer again. And you will get the urge. Computers can be downright seductive, especially to people who have gotten this far in this book.
Memory volatility In most computers, the memory is volatile.This means that it requires a source of power to be maintained. If you switch the computer off, or if there’s a power failure, you’ll lose all the data in the memory. This problem can be avoided if the memory chips are supplied with power continuously. Some machines have rechargeable memory backup batteries that keep memory data intact for short periods if there is a power failure. In contrast to memory, the data on magnetic disks, or on optical media, will stay put when the power is removed. When you’re working on a file, it is wise to store the file every few minutes on the hard drive and/or diskette. That way, in the rare event a power failure does occur, you won’t lose much work. The display The visual interface between you and your computer is known as the display. In desktop computers, an external display is often called a monitor. A cathode-raytube (CRT) monitor resembles a television set without the tuning or volume controls. A liquid-crystal-display (LCD) is lightweight and thin. This type of display is used in notebook and portable computers. It has become increasingly popular for desktop computers because the technology has improved and has become somewhat less expensive.
Showing detail The image resolution of a computer display is important. This is the extent to which it can show detail: the better the resolution, the sharper the image. Resolution can be specified in terms of dot size or dot pitch. This is the diameter, in millimeters
(mm), of the individual elements in the display—the “smallest unbreakable pieces.” A good display has a dot pitch that is a small fraction of a millimeter. A typical CRT has a dot pitch of 0.25 or 0.26 mm. The smaller the number, the higher the resolution and, all other factors being equal, the crisper the image in an absolute sense. Image resolution can be specified in a general sense as a pair of numbers, representing the number of pixels(picture elements) the screen shows horizontally and vertically. For a particular screen size, the greater the number of pixels the unit can display, the crisper the image. In personal computers, typical displays have either 800 600 resolution (800 pixels wide by 600 pixels high) or 1024 768 resolution. A few can work up to 1600 1200. Older computers often work at 640 480. Screen sizes are given in terms of diagonal measure; a popular size is the so-called 17-inch CRT (which actually has a viewable display measure of about 15.5 inches). This will work quite well at 800 600 pixels. For higher pixel dimensions, a larger screen is preferable, such as 19 or even 21 inch, but CRTs that size are rather expensive, can easily take up most of the surface of your desk, and can weigh 50 to 100 pounds. A small “15-inch” CRT (with viewable display measure of 13 to 14 inches) is sufficient if you intend to work at 640 480 pixels. A high-end display is crucial for doing graphics work, when using the Internet, in remote-control robotics, and in computer games. Besides these practical advantages, a sharp display is more pleasant to work with than a marginal one. Along with memory and hard drive capacity, the display is one of the most important parts of a computer from a user-friendliness standpoint. On the job, long hours at a computer can get tedious even if the machine is perfect. An inadequate display can give rise to eye strain and headaches and can also degrade the quality and accuracy of work done by people using the computer.
Choice of display Some computer users can get along with one display until it wears out. If you use your computer only for text-based applications, you’ll probably find a modest 15inch monitor adequate for your needs. But if you find yourself scrolling left and right because you work with lines longer than 80 characters or because the program you just purchased assumes you have a larger monitor, it’s a good idea to upgrade. If you have to squint to see tiny images on screen, likewise, you should think about enlarging the image rather than wearing eyeglasses (unless you really need glasses). If you’re buying a whole new computer system, this is a good time to buy the best monitor you can afford. Many new desktop computers are sold with monitors, but some are not, allowing you to choose your own. In that case, again, you must be sure the monitor is compatible with the rest of the system. If you’re buying a notebook computer, you’ll have options between less expensive and more expensive displays. The best way to decide what you want is to look at several displays in the store. Side-by-side comparisons can be especially revealing. Some displays can show more colors than others. The color resolution of a monitor is quoted as a number, such as “256 colors,” “thousands of colors,” or “millions of colors.” Color specifications are somewhat oversimplified, because color has two distinct properties, called the hue and the saturation. The hue is technically represented by the peak wavelength, but more often is described in terms of words (red, orange,
yellow, green, blue, indigo, violet). Saturation is the “richness” of color; the higher the saturation, the more intense a given hue appears. The “techies” use numbers from 180 to 180 to represent hue, and from 0 to 100 to represent saturation. Another way to specify color is according to the red/green/blue (RGB) scheme, in which each color has an intensity number independent of the other two, and ranging from 0 to 255, corresponding to the binary number range 00000000 to 11111111. Interlacing (or lack thereof) is important in a desktop monitor. A noninterlaced monitor is better than an interlaced one if you’re working with fast-moving graphic images. Interlacing translates into a lower refresh rate (number of times the entire image is renewed). A low refresh rate can cause noticeable flickering in the image, and can be especially disruptive in applications where rapid motion must be displayed. A good refresh-rate specification is 70 Hz or more. For applications not involving much motion, 60 or 66 Hz is adequate for some people, but others complain of eye fatigue because they can vaguely sense the flicker. Most people find 56-Hz refresh rates too slow for comfort in any application. If you’re concerned about the extremely-low-frequency (ELF) electromagnetic fields produced by CRT monitors, you might consider buying a unit that has been designed to reduce this “radiation” or buying a stand-alone LCD display panel instead (LCDs do not emit significant ELF). There is disagreement among experts as to the actual danger posed by ELF emission. It’s a good idea to arrange your workstation so your eyes are at least 18 inches away from the screen of a CRT monitor, and if you are working near other computer users, workstations should be at least 3 feet apart. The printer A computer printer is an electromechanical device that produces hard copy (text and images on paper). The most common printers are dot-matrix, thermal, inkjet, and laser.
Dot-matrix printers The “horse and buggy” of the printing family is the dot-matrix printer. This type of printer is the least expensive, in terms of both the purchase price and the long-term operating cost. Dot-matrix printers produce fair print quality for most manuscripts, reports, term papers, and theses. The mechanical parts are rugged, and maintenance requirements are minimal. Older dot-matrix printers are noisy in operation; newer machines are quieter. But none of them have the typeset-grade image quality of more expensive printers. Dot-matrix printers can render some simple graphic images, but the quality is fair at best, and it can take a long time to print a single image. Dot-matrix printers cannot reproduce detailed artwork or photographs with acceptable quality.
Thermal printers Athermal printeruses temperature-sensitive dye and/or paper to create hard copy text and images. Some thermal printers produce only black-and-white images, while others can render full color. Thermal printers are often preferred by traveling executives
who use portable computers, because these printers are physically small and light. A simple gray-scale thermal printer employs special paper that darkens when it gets hot. The print mechanism works something like that of a dot-matrix printer. But instead of the print head pressing ink onto the page, the pins in the print mechanism are heated, and they cause the paper to darken. A color thermal printer uses thick, heat-sensitive dyes of the primary pigments: magenta (pinkish red), yellow, and cyan (bluish green). Sometimes black dye is also used, although it can be obtained by combining large, equal amounts of the primary pigments. The print head uses heat to liquefy the dye, so it bleeds onto the paper. This is done for each color of pigment separately. There are three separate, overlapping images produced, one for each primary pigment. Some, if not most, thermal printouts fade after awhile. Have you ever pulled out an old store receipt and found that it was washed-out or blank? Thermal printers can be convenient in a pinch, but you should be aware that they have this problem—and it’s not restricted to old machines. In fact, stores and even some post offices seem to be installing brand new printers with this “feature” more and more. If you’re keeping a receipt for tax purposes or for proof-of-purchase and you notice that it has been printed on thermal paper, go to a print shop and make a photocopy of the receipt right away. How can you recognize a thermal printout? The paper curls up when it’s fresh out of the machine.
Inkjet printers In an inkjet printer, tiny nozzles spray ink onto the paper. Some inkjet printers are almost silent; others make strange, intermittent, loud beeps and clicks. Most of these printers are comparatively slow to produce an image, and the ink needs time to dry even after the image comes out, but the quality can be excellent. Inkjet printers are available in single-color and multicolor designs. The best color machines produce photographlike images. A high-end inkjet printer costs roughly twice as much as a high-end dot-matrix machine, although some monochrome inkjets are as inexpensive as dot-matrix printers. Inkjet printers require periodic replacement of the ink cartridges. There are three or four of these, containing cyan, magenta, yellow, and sometimes black ink. Inkjet printers need a certain kind of paper; some papers have fibers that carry the ink along via capillary action, causing characters and images to blur. The finest, most expensive “bond” for typing might prove disastrous if used with an inkjet printer. If you have doubts, read the instruction manual or call the manufacturer of the printer.
Laser printers
A laser printer works like a photocopy machine. The main difference is that, while a photocopier creates a copy of a real image (the paper original), a laser printer makes a copy of a digital computer image. When data arrives at the printer from the computer, the encoded image is stored in the printer’s memory. The memory stores one page of data, and then sends it along to the laser and other devices. Some printers use a light-emitting-diode (LED) matrix, rather than a single laser. These printers are called LED printers. For practical purposes, LED printers are equivalent to laser printers.
The laser blinks rapidly while it scans a cylindrical drum. The drum has special properties that cause it to attract the printing chemical, called toner,in some places but not others, creating an image pattern that will ultimately appear on the paper. A sheet of paper is pulled past the drum and also past an electrostatic charger. Toner from the drum is attracted to the paper. The image thus goes onto the paper, although it has not yet been permanently fused, or bonded, to the paper. The fuser, a hot pair of roller/squeezers, does this job, completing the printing process. The main asset of laser printers is their excellent print and graphics quality. The image resolution of a laser printer ranges from about 300 dots per inch (DPI) for older units to 1200, 2400, or even more DPI in state-of-the-art machines. As far as the untrained eye can tell, 600 DPI is as good as a photograph. Laser printers can handle graphics and text equally well. If an image can be rendered on a photocopy machine, it can be rendered just as well on a laser printer. Another asset of laser printers is that they make almost no noise. Yet another good feature is that this type of printer is relatively fast. The best highend machines can produce a couple of dozen copies per minute. The laser printer is the best device for rendering high-resolution hard copy text and graphics. If you’re doing desktop publishing, presentation graphics, or anything else that requires top-grade or high-volume hard copy, you’ll want a laser printer. Ask some friends for their opinions, and if printing is really important to you, don’t cut corners. A good laser printer is the “geek’s” equivalent of a reliable truck. The modem The term modem is a contraction of modulator/demodulator. A modem interfaces a computer to a telephone line, television cable system, fiber-optic network, or radio transceiver, allowing you to communicate with other computer users and to “surf the Internet.”
External versus internal An external modem is a self-contained unit (box) that you can use with any computer. It has a cord that runs to the computer’s serial data port(also called the communications port) and another cord that runs to the telephone jack. The modem will probably also have a jack into which you can plug your phone set. Aninternal modemis a printed-circuit board, also called a card,that is commonly installed in new computers. Virtually all desktop computers come with modems. A new notebook computer might not have an internal modem installed; in that case you can purchase one in the form of a PC card that fits into a slot on the side of the computer. This card is roughly the height and width of a credit card, but somewhat thicker.
Digital versus analog A computer works with binary digital signals, which are rapidly fluctuating direct currents. For digital data to be conveyed over a telephone or radio circuit, the data must be converted to analog form. In a telephone modem or radio-transceiver modem, this is done by changing the digit 1 into an audio tone, and the digit 0 into another tone with a different pitch. The result is an extremely fast back-and-forth
alternation between the two tones. In modulation, digital data is changed into analog data. It is a type of digital-to-analog(D/A)conversion. Demodulationchanges the analog signals back to digital ones; this is analog-to-digital (A/D) conversion. If you happen to pick up a telephone extension while someone is on-line with the computer from another extension, you’ll hear the analog signals from the two modems; it sounds like a hiss or roar. But don’t make a habit of doing this. It can cause the computer to be disconnected from the on-line network.
Data speed Modems work at various speeds, usually measured in bits per second(bps). You will often hear about kilobits per second (kbps), where 1 kbps 1000 bps, or megabits per second (Mbps), where 1 Mbps 1000 kbps. Sometimes you’ll hear about speed units called the baud and kilobaud. (A kilobaud is 1000 baud.) Baud and bps are almost the same units, but not they are not identical. People often use the term baud when they really mean bps. The higher the speed as specified in bps, the faster the data is sent and received through the modem. Speeds keep increasing as computer communications technology advances. Modems are rated according to the highest data speed they can handle, in bits per second (bps), kilobits per second (kbps), or megabits per second (Mbps). A typical “telephone modem” works at about 56 kbps. Digital-subscriber-line (DSL) modems work somewhat faster, around 128 kbps. Television cable modems can work upward of 1 Mbps.
Basic components of a modem Figure 33-4 is a block diagram of a modem suitable for interfacing a home or business computer with the telephone line. The modulator, or D/A converter, changes the digital computer data into audio tones. The demodulator, or A/D converter, changes the incoming audio tones into digital signals for the computer. The audio tones fall within the frequency range, or band, of approximately 300 Hz to 3 kHz. This is the band needed to clearly transmit a human voice. It’s amazing how much computer data can race over a single telephone or radio circuit having such a narrow bandwidth. Even pictures can be sent and received in brilliant color and in quite good detail (high resolution). As you might imagine, color images take longer than gray-scale images to send and receive; also, the more detail an image contains, the longer it takes to be transferred at any given data speed. The Internet The Internet is a worldwide system, or network, of computers. It got started in the late 1960s, originally conceived as a network that could survive nuclear war. Back then it was called ARPAnet, named after the Advanced Research Project Agency (ARPA) of the United States federal government.
Protocol and packets When people began to connect their computers into ARPAnet, the need became clear for a universal set of standards, called a protocol, to ensure that all the machines “speak the same language.” The modern Internet is such that you can use any type of computer—IBM-compatible, Mac, or other—and take advantage of all the network’s resources. All Internet activity consists of computers “talking” to one another. This occurs in machine language. However, the situation is vastly more complicated than when data goes from one place to another within a single computer. In the Internet (often called simplythe Net), data must often go through several different computers to get from the transmitting or source computer to the receiving or destination computer. These intermediate computers are called nodes, servers, hosts, or Internet service providers (ISPs). Millions of people are simultaneously using the Net; the most efficient route between a given source and destination can change from moment to moment. The Net is set up in such a way that signals always try to follow the most efficient route. If you are connected to a distant computer, say a machine at the National Hurricane Center, the requests you make of it and the data it sends you, are broken into small units called packets. Each packet coming to you has, in effect, your computer’s name written on it. But not all packets necessarily travel the same route through the network. Ultimately, all the packets are reassembled into the data you want, say, the infrared satellite image of a hurricane, even though they might not arrive in the same order they were sent. Figure 33-5 is a simplified drawing of Internet data transfer for a hypothetical file containing five packets transferred during a period of extremely heavy usage. Nodes are shown as black dots surrounded by circles. In this example, some packets pass through more nodes, and/or over a much greater physical distance, than others. If Net traffic were very light, all the packets might follow the same route through fewer nodes. This is why it takes longer to acquire data on the Net during peak hours of use, as compared with times when there are comparatively few people connected into it. A file cannot be completely reconstructed until all the packets have arrived and the destination computer has ensured that there are no errors.
E-mail and newsgroups For many computer users, communication via Internet electronic mail (e-mail) and/or newsgroups has practically replaced the postal service. You can leave messages for, and receive them from, friends and relatives scattered throughout the world.
To effectively use e-mail or newsgroups, everyone must have an Internet address. These tend to be arcane. An example is
sciencewriter@nanosecond.com
The first part of the address, before the @ symbol, is the username. The word after the @ sign and before the period (or dot) represents the domain name. The threeletter abbreviation after the dot is the domain type. In this case, “com” stands for “commercial.” Nanosecond is a commercial provider. Other common domain types include “net” (network), “org” (organization), “edu” (educational institution), and “gov” (government). In recent years, country abbreviations have been increasingly used at the ends of Internet addresses, such as “us” for United States, “de” for Germany, “uk” for United Kingdom, and “jp” for Japan.
Internet conversations You can carry on a teletype-style conversation with other computer users via the Internet, but takes a bit of getting used to. When done among users within a single service provider, this is called chat. When done among people connected to different service providers, it is called Internet relay chat (IRC). Typing messages to and reading them from other people in real time is more personal than letter writing, because your addressees get their messages immediately. But it’s less personal than talking on the telephone, especially at first, because you cannot hear, or make, vocal inflections. It is possible to digitize voice signals and transfer them via the Internet. This has given rise to hardware and software schemes that claim to provide virtually toll-free long-distance telephone communications. As of this writing, this is similar to amateur radio in terms of reliability and quality of connection. When Net traffic is light, such connections can be good. But when Net traffic is heavy, the quality is marginal to poor. Audio signals, like any other form of Internet data, are broken into packets. All, or nearly all, the packets must be received and reassembled before a good signal can be heard. This takes variable time, depending on the route each packet takes through the Net. If many of the packets arrive disproportionately late, and the destination computer can only “do its best” to reassemble the signal. In the worst case, the signal might not get through at all.
Getting information One of the most important features of Internet is the fact that it can get you in touch with thousands of sources of information. Data is transferred among computers by means of a file transfer protocol (FTP) that allows the files on the hard drives of distant computers to become available exactly as if the data were stored on your own computer’s hard drive, except the access time is slower. You can also store files on distant computers’ hard drives. When using FTP, you should be aware of the time at the remote location, and avoid, if possible, accessing files during the peak hours at the remote computer. Peak hours usually correspond to working hours, or approximately 8:00 a.m. to 5:00 p.m. local time, Monday through Friday.
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In studying and using electronic equipment that has to do with e-Dynamic control, we need to know and be skilled in:
1. Design calculations in electronic circuits
analog, digital, analog and digital sequential control.
2. measurement using electronic tools and materials
on both mechanical objects and time responses on
electromagnetic waves are also lasers and optics
3. Observation of tools and design of e-Dynamic control equipment
especially for equipment categories that require research and
development so that the equipment and materials used can
used and functioned for the response and time period
analog, digital, analog and digital sequential control.
2. measurement using electronic tools and materials
on both mechanical objects and time responses on
electromagnetic waves are also lasers and optics
3. Observation of tools and design of e-Dynamic control equipment
especially for equipment categories that require research and
development so that the equipment and materials used can
used and functioned for the response and time period
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