The following are some basic facts about input loop power sources: The input module usually isn't a loop power source. Although 120V is common for digital loops, other voltages are also used. There ...

I/O modules are building blocks of industrial control systems used in end equipment such as PLC (Programmable Logic Controllers), PAC (Programmable Automation Controller) and DCS (Distributed Control ...

The answer is B, “+24 VDC.” A sinking digital input on a PLC I/O card is looking for positive 24 VDC at the input terminal. This configuration is most commonly used because +24 VDC at the digital ...

In our previous issue, we noted that the first step in troubleshooting digital input modules is to verify the power source of each loop. If input power is missing, the causes can be such things as ...