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Automating Manufacturing Systems - Process Control and ...

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plc electrical - 31.8<br />

31.2.1 Selecting Voltages<br />

When selecting voltage ranges <strong>and</strong> types for inputs <strong>and</strong> outputs of a PLC some<br />

care can save time, money <strong>and</strong> effort. Figure 31.6 that shows three different voltage levels<br />

being used, therefore requiring three different input cards. If the initial design had selected<br />

a st<strong>and</strong>ard supply voltage for the system, then only one power supply, <strong>and</strong> PLC input card<br />

would have been required.<br />

48Vdc<br />

24Vdc<br />

5Vdc<br />

+<br />

-<br />

+<br />

-<br />

+<br />

-<br />

PLC Input Cards<br />

I0<br />

com<br />

I0<br />

com<br />

I0<br />

com<br />

PLC Input Card<br />

+<br />

24Vdc<br />

I0<br />

I1<br />

I2<br />

I3<br />

-<br />

com<br />

Figure 31.6<br />

St<strong>and</strong>ardized Voltages

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