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Automating Manufacturing Systems - Process Control and ...

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plc pid - 25.14<br />

PID<br />

<strong>Control</strong> Block: PD12:0<br />

Proc Variable: N7:0<br />

Tieback: N7:1<br />

<strong>Control</strong> Output: N7:2<br />

Note: When entering the ladder logic program into the computer you will be able to<br />

enter the PID parameters on a popup screen.<br />

Figure 25.17<br />

PLC-5 PID <strong>Control</strong> Block<br />

PID controllers can also be purchased as cards or st<strong>and</strong>-alone modules that will<br />

perform the PID calculations in hardware. These are useful when the response time must<br />

be faster than is possible with a PLC <strong>and</strong> ladder logic.<br />

25.4 DESIGN CASES<br />

25.4.1 Oven Temperature <strong>Control</strong><br />

Problem: Design an analog controller that will read an oven temperature between<br />

1200F <strong>and</strong> 1500F. When it passes 1500 degrees the oven will be turned off, when it falls<br />

below 1200F it will be turned on again. The voltage from the thermocouple is passed<br />

through a signal conditioner that gives 1V at 500F <strong>and</strong> 3V at 1500F. The controller should<br />

have a start button <strong>and</strong> E-stop.<br />

Solution:<br />

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

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