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Automating Manufacturing Systems - Process Control and ...

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plc pid - 25.20<br />

BT9:0/DN<br />

BT9:2/EN<br />

BT9:1/DN<br />

SUB<br />

SourceA N7:80<br />

SourceB N7:42<br />

Dest N7:81<br />

DIV<br />

SourceA N7:81<br />

SourceB 2<br />

Dest N7:60<br />

Block Transfer Write<br />

Module Type Generic Block Transfer<br />

Rack 000<br />

Group 1<br />

Module 0<br />

<strong>Control</strong> Block BT9:2<br />

Data File N9:60<br />

Length 13<br />

Continuous No<br />

Figure 25.21<br />

A Water Tank Level <strong>Control</strong> Program<br />

25.5 SUMMARY<br />

• Negative feedback controllers make a continuous system stable.<br />

• When controlling a continuous system with a logical actuator set points can be<br />

used.<br />

• Block diagrams can be used to describe controlled systems.<br />

• Block diagrams can be converted to equations for analysis.<br />

• Continuous actuator systems can use P, PI, PD, PID controllers.<br />

25.6 PRACTICE PROBLEMS<br />

1. What is the advantage of feedback in a control system?<br />

2. Can PID control solve problems of inaccuracy in a machine?<br />

3. If a control system should respond to long term errors, but not respond to sudden changes, what<br />

type of control equation should be used?

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