Muhammad Faizal bin IsmailDept. of Electrical Engineering

PPD, UTHMifaizal@uthm.edu.my

013-71431061

IntroductionAnalog vs. Digital Control SystemDigital Control System SelectionSignal in Digital Control System

Outline:1. Introduction2. Analog vs. Digital Control System3. Digital Control System Selection4. Signal in Digital Control System5. Data Acquisition, Conversion & Distribution System6. Example of Digital Control System

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Outline

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 making2.One hardware design is able to be used with

many different software variations3.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.

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Analog control system Digital control system

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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4. Signal in digital control system

• Type of signals:

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Continuous-time analog signal Continuous-time quantized signal

Sampled-data signal Digital signal

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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