1762-IF4 Reading High

I have a RM Young temp/RH sensor connected to my 1762-IF4 with a MicroLogix 1400. The sensor is a powered device with a singe ended 4-20mA output. Using a meter, I measured the sensors output at 12mA, which was correct. However, when I connect it to the IF4 module, the PLC reads it at 15mA. Has anybody seen this type of anamoly before? I have not had a chance to check the card's inputs with a signal generator, so I can't rule that out at the moment. Thanks.

What do to read on your meter with the sensor connected to the PLC and your meter in series with the input card? Can you give us a drawing of how you connected it?

With the meter in series with the PLC input and the sensor, I still read the increased amperage. I will try to explain how I connected it, since I don't have a drawing at the moment. My 24 VDC source is powering both the PLC and the sensor. The signal from the sensor is connected to the IN+ terminal on the IF4 card. The IN- terminal is connected to the DC common.

Is the DC common grounded? You may need to install an isolator between your Temp transmitter and the input.

Sorry, but I don't see the difference between the pdf and what I described. I did connect it according to the 3 wire diagram in the pdf. I don't recall if the DC com is grounded, i'll have to check on Monday.

I have seen issues like this when there are more then one power source connected to the input card.