AB PLC 4-20mA no response from PLC

[balash]

I might have to make a converter.

actually you don't need a converter, just a 250 ohm between voltage inputs

done that many times cause integrated inputs on small plc's are usually voltage

 

[bernie_carlton]

A test would be to wire a precision 500 ohm resistor (at least 1/2 watt) from the VOLTAGE input to common then wire the current signal also to that voltage input. The voltage drop across the 500 ohm resistor at 20 ma would provide 10 volts. (The 250 ohm resistor suggested by Balash would yield up to 5 vdc at the 20 ma point.)

Actually, disconnect from the input module and just wire the resistor from the analog output of the device to the 24 volt supply common then measure across it with varying temperatures. You should see a low to high voltage (max 10 volts) with higher temperatures. If this works out then attach the setup to the voltage input on the PLC.

Regarding possible damage, the PDF for the similar stand-alone card notes that possibility, especially if a voltage input was applied to the current terminal.

 

[plimpyd]

Thanks to both of you! I'm currently doing a project as a student and got this PLC second hand. I never had to use the analog current inputs until recently, hence the reason I've been so confused. I'll resort back to the voltage inputs and that should be enough to get me through! I can't express how grateful I am and if I have any issues or even some luck I'll try and find time to come back and let you know my results!

 

[mdim]

It's either the analog inputs are turned off or someones blown them up somehow.

Did you try with channel 2&3? As I see they are disabled. Still I think it takes much effort to burn 4oo4 inputs.

 

[balash]

The 250 ohm resistor suggested by Balash would yield up to 5 vdc at the 20 ma point.

yes, quite right. i've been recently looking into ABB's analog input wiring that has 250 internally wired for current input (to convert it to 1-5V internally) so that must have been on my mind