Hello.
I have typically run current measurements with a 250 ohm resistor to convert to voltage, but have always done so in differential, and with two 11 kohm bias resistors, one on each wire. However, I am now forced into using RSE due to a lack of channels, and I have 5 thermocouples which need to go over to RSE. Due to this, I have set them up through a temperature transmitter each. You will find an image of the exact layout attached. They are on a 24v battery, and the battery's negative side is connected to the DAQ's chassis grounding point, which seems to be directly connected to the AI GND line. The BNC connector at the panel is then connected to a junction box, which then connects to the DAQ.
Everything is seemingly fine, but there is an offset, which I cannot seem to trace down. I had originally had an 11 kohm bias resistor on the line from the transmitter, but removed it, knowing that it causes an offset, but still didnt find myself at the expected value. According to my Fluke, it should have been reading 12 degrees C, but I was getting just 4, which was the value at all 5 transmitters. Now, the range on the transmitter is from -32 C to 1000 C, but I typically have errors of just a degree or two at this area. It should be noted that the actual length of the thermocouples are only about two meters, and I even attached a little stub which was only about 2cm long to try to see if it was picking up common mode noise.
Have I perhaps done something wrong? Is there a minor ground loop that I am not seeing, or something? Just to be clear, each resistor was ohmed out with my Fluke at 250 ohms, and the datasheet shows a tolerance of +- 0.1%.
