Temperature Measurement using Iex Thermistor with PCI 6259

[BryanL]

Hello All,

I am having some difficulty measuring temperature using MAX with Iex Thermistor setup, and would like to know if I have missed any thing important. I am using external current excited thermistor with 2 wire configuration and PCI 6259 card with MAX.

This is a channel that was originally configured to Voltage measurement and MAX measures about 900mV from this channel OK, the voltage converts to Temperature to be around 30C. Then I added a new channel and configured it to measure temperature directly using MAX default Iex Thermistor setup. This is when the problem show up: I will get a constant -273C instead of 30C as expected when run the channel in MAX. I must have been doing something wrong here.

Your help is greatly appreciated!

Bryan

[RavensFan]

Are you sure the coefficients of A, B, C used in the DAQmx task for thermistor match those given by the manufacturer of the thermistor?

Is the issue with trying to read 2 thermistors at the same time vs. 1?  Or is it a case of reading 1 thermistor using the temperature Max settings isn't working vs. reading the thermistor using a voltage setting?

Message Edited by Ravens Fan on 07-25-2009 12:13 AM

[BryanL]

Hi Ravens, thank you for taking the time on this problem.  I am sure the issue was not caused by the A, B, C parameters being wrong, as when I ran the channel in MAX, I am getting a constant -273.15 value, and it was not updated as a real measurement.

To your 2nd question, this is a case of measuring 1 thermistor value using the Iex Thermistor method vs. Voltage measurement.  If I set it up to measure Voltage directly, I can see the realtime updates of the measurement values of voltage, which converted to Temperature in my VI to be reasonable values of temperature.

Bryan

[BryanL]

Hi...was wondering anyone had a similar issue? A possible issue with MAX driver? I was using the following Steinhart parameters:

A: 1.129241e-3, B: 2.341077e-4, and C: 8.775468e-8.  This is a 10K resistance Thermistor with external current source of 100uA.  

Thanks in advance for any suggestions.

Bryan

[BryanL]

Also forgot to mention that I am using MAX 4.5

[BryanL · Accepted solution]

We found out that the issue was caused by our wiring of thermistor NOT using Differencial setup. If Differencial was used, the MAX convertion worked fine. If not, only directly Voltage measurement will work.  Bryan