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Automating Manufacturing Systems - Process Control and ...

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plc pid - 25.17<br />

25.4.2 Water Tank Level <strong>Control</strong><br />

Problem: The system in Figure 25.19 will control the height of the water in a tank.<br />

The input from the pressure transducer, Vp, will vary between 0V (empty tank) <strong>and</strong> 5V<br />

(full tank). A voltage output, Vo, will position a valve to change the tank fill rate. Vo varies<br />

between 0V (no water flow) <strong>and</strong> 5V (maximum flow). The system will always be on:<br />

the emergency stop is connected electrically. The desired height of a tank is specified by<br />

another voltage, Vd. The output voltage is calculated using Vo = 0.5 (Vd - Vp). If the output<br />

voltage is greater than 5V is will be made 5V, <strong>and</strong> below 0V is will be made 0V.<br />

Digital<br />

to Analog<br />

Converter<br />

Amp<br />

PLC<br />

Running<br />

<strong>Control</strong><br />

Program<br />

Water<br />

Supply<br />

Analog<br />

to Digital<br />

Converter<br />

Amp<br />

Water Tank<br />

pressure<br />

transducer<br />

Figure 25.19<br />

Water Tank Level <strong>Control</strong>ler

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