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Analog Input Error


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I have an analog input issue I was hoping someone could help me out with.

I am using module # UIDWCB1 which has two analog inputs.

I have a  two 4-20ma transducer (0-20,000PSI).  I have setup analog input 0 and 1 as shown below.

Analog input 1 seems to be running correct as I am receiving a value of 0 when no pressure is applied. However the pressure transducer in analog input 0 is not. The red LED  turns on and indicates an overflow and I am seeing a reading of just over 20,000. At first I thought I had an issue with the one transducer but I have switched the transducers around and whichever one is in AI1 works correctly. 

Both transducers give the same value in AI0 and the red LED comes on instantly.

I have fought with this for a couple hours now and cant seem to figure out why it works correctly in AI1 but not AI0. Has anyone ran into this problem before?




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Could it be a wiring problem? Sounds like that...

Try to put your transducers on a test wiring as close to the AIs as you can.

Another clue is bad/incorrect reference to the system 0V or 24V somewhere in the system. That, not necessarily has to be close to AIs. It could be as far as any voltage fed back in into digital outs. Unistream is quite sensitive on that.
Check everything - any voltages should be where they're supposed to be and shouldn't where the they're not.

Disconnecting as much as you can from the PLC and then step-by-step putting everything back could be helpful as well.

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  • MVP 2023

Are the sensors loop powered or do they have separate power and source the signal to the module.  Tell us what you have - manufacturer and model number.

Put a meter in series with the analog input and read the actual current.  If the sensors are sourcing the signal, you may have a ground potential difference between the module and the sensor.

Joe T.

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