Problem with reading an unusual value from a FP-RTD-124 module.

[Ken W.]

I need help troubleshooting a FP-RTD-124 module. The problem I am having is that when I monitor the channel in FieldPoint Explorer, I get what appears to be a random number for the value. The numbers range from around -40C to +50C. I would expect the value to be consistent since it should be room temperature. FP Explorer also indicates that the channel status is "Successful!" and the rest of the channels are "Open RTD".

I am convinced that the RTD is wired in correctly to Channel 0 of the FP module. I have pulled the RTD out and measured consistently (using a multimeter) the resistance at ~107.4 Ohms which is what I would expect at room temperature. I have also tried changing the RTD and using diff
erent channels but I am still receiving those random numbers for the value. In addition, I made sure the channel was configured with the same TCR value as the RTD.

--- Additional Information ---
The RTD is a 4 wire Minco 100 Ohm Platinum RTD with a TCR=0.00385. I am using FieldPoint Explorer 3.0.2 (build 177). The network module is a FP-1600 connected directly to a computer using a x-over ethernet cable. The terminal base for the FP-RTD-124 is a FP-TB-1.

Any help would be appreciated.
Ken

[Aaron_G]

Ken,

The first thing to do is to make sure the FP-RTD-124 is working correctly. Take a fixed resistor (100-200 ohms) and wire it between +Sense and -Sense. Add one jumper wire from +Sense to +Excite and a second one between -Sense to Com. Set the channel to the 0-400 Ohm range in FieldPoint Explorer. If the resistance is a steady, accurate value then the FP-RTD-124 is fine and you need to double check the RTD itself. If the reading is jumping around on the FP-RTD-124, then there is either an outside source of influence (make sure there are no connections to the V & C terminals on the terminal base) or the FP-RTD-124 has been damaged. If the FP-RTD-124 is behaving correctly, then check the lead to lead resistance on your RTD. It may be that one of the wires is
partially open that you did not catch when measuring with the DMM (assuming you used a 2 wire DMM).

Regards,
Aaron

[Ken W.]

Thanks Aaron for responding. I did wire a resister and jumpers on another channel according to your comment but it did not help. The temperature and resistance readings are still jumping all over the place. The RTD-124 is powered by the network module (not by connections to the V & C terminals). There is nothing near the FP modules that could cause interference either. As for the RTD itself, I tested it using an Omega RTD reader and it checked out fine. If you or anyone else has anymore ideas I would be glad to hear it.

Thanks,
Ken

[Aaron_G]

Ken,

If the readings are that sporadic with a fixed resistor when no other channels are wired and there are no connections to the V & C terminals, then the module has most likely been damaged and you should contact NI for an RMA to have the module repaired. However, it sounds like you still have other channels wired, so try disconnecting all channels except the fixed resistor first. Then add the channels one at a time until the problem starts. If the problem persists even when all channels except the fixed resistor are disconnected, contact NI support to arrange for an RMA. This can be done at www.ni.com/ask

Regards,
Aaron