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Analog Ouput/Input

Analog Ouput/Input

Analog Ouput/Input


I'm usually confuse on how to tell if a particular device gives an analog input to the PLC or does it need an analog input from the PLC (hence PLC output). I usually get my way around by talking to the vendor. By looking at it based on the drawings e.g. for the kinetrol actuator that I'm working on (need to create the loop diagram), it requires 4-20mA for its positioner signal and angle re-transmit supply (see attachment).

How do you guys figure out which one is the analog output and which one is the input? Or are they all input to the PLC?


RE: Analog Ouput/Input

I'd say yes to both. It takes an analog signal from the PLC to drive the positioner and provides feedback to the PLC about the position has been attained. It's hard to make out, but it looks like the microprocessor reads the A/D convertor to close the loop internally. So at the PLC if you command a position that command can be compared to what actually happened so that an alarm or other action can be taken if the two don't match closely enough. Or you can ignore the feedback and hope the positioner gets to where it was told to go.

RE: Analog Ouput/Input

The top two terminals receive a position command signal from a PLC analog output that provides 4-20 mA - that's why it is called Signal In.

The bottom two terminals send a 4-20 mA signal to a loop-powered (i.e., two-wire) PLC analog input indicating the position of the unit - that's why it's called Position Feedback.

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RE: Analog Ouput/Input

The positioner relies on the 4-20 mA input signal to operate (thus 'loop powered'). The 4-20 mA retransmit output is optional. Assuming the positioner is operating correctly, when you apply a signal, say 12 mA, or 50%, then the positioner should eventually reach that position, and the retransmit output will be a proportional signal to verify the position back to the control system. This would be handy if there is a likelihood that the positioner could bind, fail on loss of air pressure, or the like. If that's not something you need, then you'll only need to connect the controller output to the positioner input terminals.


It's all okay as long as it's okay.

RE: Analog Ouput/Input

Thanks for the input guys, 'appreciate it!

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