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Chapter 3 Digital Control System
Eddy Irwan Shah Bin SaadonDept. of Electrical EngineeringPPD, [email protected], G3 , FKEEExt : 8519
Outline:
1. Introduction
2. Analog vs. Digital Control System
3. Digital Control System Selection
4. Signal in Digital Control System
5. Data Acquisition, Conversion & Distribution System
6. Example of Digital Control System
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1. Intro - Objective of this chapter
After completing this chapter you will be able to:
Differentiate between analog and digital control system
Explain the reason for using digital control system
Understand the operation involved in digital conversion system
Describe the sampling method
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Cont.
Digital control system employs digital computer, microcontroller and microprocessor
Example: electromechanical servomechanism in aircraft, automobiles, mass-transit vehicle, oil refineries, paper making machine and household appliances
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Cont.
Advantages:
1. Increase flexibility of the control programs and the decision making
2. One hardware design is able to be used with many different software variations
3. Simplifying and reducing design time
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2. Analog Vs Digital
The basic knowledge to distinguish analog and digital system is the type of signals processed
Analog system processes continuous signals whilst digital system processes discrete signals
Following is an example of block diagram for both of the systems
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Cont.
Analog control system Digital control system
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3. Digital Control System Selection
Control system was developed from analog (continuous-time) devices such as operational amplifiers, capacitors, inductors, resistors and mechanical components.
However, digital control system has been used widely since it was introduced and analog control system are used nowadays for a simple applications.
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Cont.
Even though digital control system cannot perform integration of basic control system function, it has been used widely due to:
1. Cost2. Communication3. Flexibility4. Digital interfacing devices5. Performance6. Diagnostics
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Exercise 1
Discuss each of the aspects why digital control system are preferred compared to the analog control system.
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4. Signal in digital control system
Type of signals:
Continuous-time analog signal Continuous-time quantized signal
Sampled-data signal Digital signal11
Cont.
Continuous-time analog signal = a continuous range of time signal where the amplitude is continuous range of values
Continuous-time quantized signal = continuous range of time signal where the amplitude is a finite number of distinct values
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Cont.
Sampled-data signal = a discrete-time signal where the amplitude is in continuous range of values
Digital signal = discrete-time signal with quantized amplitude and can be represented by sequence of number
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Cont.
Signal form in digital control system
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Cont.
Sample and hold (S/H) and Analog-to-digital (A/D) converter convert the continuous-time signal into a sequence of numerical coded binary words (coding/ encoding)
The digital computer receives the data and produces a new sequence of numbers with defined algorithm and send it to Digital-to-analog (D/A) converter
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Cont.
D/A converter will then convert the sequence of number in numerical code into a continuous-time signal
The-real time clock in the computer will synchronizes the event
The output form D/A converter is hold by Hold circuit to establish a distinct continuous-time signal
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Cont.
The signal is fed to the plant directly or through actuator to control its dynamics
The plant output continuous-time signal is detected by a transducer for a closed-loop system as a feedback to the system and compared to the input signal where the signal is received by S/H and A/D converter as an input
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