cDAQ 9171 Thermistor Temperature Incorrect

[diagnosticAZ]

I am using a cDAQ 9171 hooked up via USB to my computer for the purpose of measuring the temperature from a thermistor.  I have selected Iex as the thermistor type, inputed my A,B,C values and every other parameter.  The thermistor works, however the readings seem to be off by about 100 degrees C.  Do you know what could be causing this?

Thank you.

[SSPTest]

Hi,

I'm sorry to hear you are having trouble getting the expected measurement with your thermistor. Just a couple questions:

- what module are you using to measure this?

- how do you have the thermistor wired to this module?

- are you using LabVIEW or NI MAX to take this reading? If you aren't already, I would suggest starting with NI MAX and either setting up a task in there or using test panels to see what measurement you get, this takes any possible coding errors out of the picture.

- finally, what temperature range are you trying to read within?

Please let me know the answers to these questions then hopefully I can provide some more directed troubleshooting steps. Thanks!

[TheEngineeringBear]

Also testing the thermistor's without them being attached to anything might not be a bad idea.  How new are the thermistor's you are working with?

-Bear

[TheEngineeringBear]

Any update with this?

-Bear

[diagnosticAZ]

Hi,

After a lot of trouble shooting, it sounds like the cDAQ 9171 with the 9211 card isn't suited for thermistors. I am using a 2-wire thermistor of diameter 0.5mm, temp range of 18-37C, tolerance of 0.5%.  The thermistor itself works as I tested it with my multimeter for resistance at room temperature - it matched the specs provided by the manufacturer.

I was able to get the thermistor to work after building my own voltage divider circuit and using a standard NI DAQ analog input with a 5V source. 

[TheEngineeringBear]

Yes, sorry you had to find that out on your own! 

The NI 9219 is the module for Thermistor measurements.  But, you found the round about route to doing it.  Because you have to power the thermistor I assume you did some tricks with the circuit so you could power and read the voltages on the thermistor.

Choosing an RTD or Thermistor Measurement System

http://www.ni.com/white-paper/3643/en/

Good luck!

-Bear