errors with accurate readings on nickel rtd

[Daddy-O]

I am using a 120Ohom Nickel RTD and CFP-RTD-122.

I have a VI-that converts direct Impedence measurements and converts it into degrees C. It works great, based on all of the charts I have regarding Nickel RTD,s and if I plug values into it, it works fine. When I bring up the MAX for the 122 It is reading the wrong values. I have checked (with meter) the values I get in ice-water, hot coffee, etc. ANd the RTD is generating the correct impedence. However, my FFP Module does not see the correct values. I only have one RTD plugged into this module.

I have programatically changed the range to reflect the zero to 400 Ohm Range.

Chris

[Jonathan_C]

Hi Chris,

Is this a two wire or a three wire RTD?  If it is a two wire RTD, did you connect the SENSE and the COM port using a short jumper wire?  What kind of excitation does this RTD require? The EX+ terminal provides a 0.25 mA excitation current. Also, what kind of values are being read in MAX?  Are these values close or are they completely off?  Do the readings fluctuate or do they stay steady but innacurate?

[Daddy-O]

Hi Jonathan,

It's a 3-wire, from an unknown manufacturer, so I'm not really sure of the required excitation. I have hooked it up with the 3 wires, and with the 2 "low" wires tied together and a jumper, and that doesn't change. I did have help from NI help desk and they duplicated my setup with a "Minco" rtd and didn't have the error, so I am desperately trying to get in touch with Minco to select the RTD I need and get some samples. I will know in the next 2 days what the issue is. I am 99% sure that it is this unknown RTD that is causing the issue.. When I wire various value fixed resistors, I get exactly the temp I am expecting. OH, the RTD doesn't vary at all (much) and it seems to be about 40% of what I expect the temp to indicate. I think I am in wait and see mode right now, until I get the "known" RTD's in here, thanks for your response, and I will let you know what happens,

Chris