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Automating Manufacturing Systems - Process Control and ...

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plc pid - 25.11<br />

I:001/1 - START<br />

B3/0<br />

I:001/0 - ESTOP<br />

B3/0 - ON<br />

B3/0 - ON MOV<br />

Source 0<br />

Dest N9:60<br />

B3/0 - ON<br />

BT9:2/EN<br />

BT9:1/DN<br />

SUB<br />

SourceA N7:80<br />

SourceB N7:42<br />

Dest N7:81<br />

MUL<br />

SourceA N7:81<br />

SourceB 2<br />

Dest N9:60<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 25.12<br />

Implementing a Proportional <strong>Control</strong>ler with PLC-5 Ladder Logic<br />

This controller may be able to update a few times per second. This is an important<br />

design consideration - recall that the Nyquist Criterion requires that the actual system<br />

response be much slower than the controller. This controller will only be suitable for systems<br />

that don’t change faster than once per second. (Note: The speed limitation is a practical<br />

limitation for a PLC-5 processor based upon the update times for analog inputs <strong>and</strong><br />

outputs.) This must also be considered if you choose to do a numerical analysis of the control<br />

system.<br />

www.PA<strong>Control</strong>.com

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