Using Thermistors in VI Logger with a Traditional DAQ DevicePrimary Software: Other NI Software>>VI LoggerPrimary Software Version: 2.0.1 Primary Software Fixed Version: N/A Secondary Software: N/A Hardware: Multifunction DAQ (MIO)
Problem: How do I use a thermistor, with its Steinhart-Hart coefficients, in VI Logger for a Traditional DAQ device? Solution: Traditional NI-DAQ Virtual Channels don't have a built in thermistor sensor type for analog input. This KB shows how to configure a custom sensor input for use with thermistors.
Thermistors have a resistance-temperature relationship which is approximated using the Steinhart-Hart equation:
Manufacturers will provide the different a, b and c coefficients for the Steinhart-Hart equation to best approximate a specific thermistor model. Obtaining temperature data via a thermistor using VI Logger and a Traditional DAQ device requires the creation of a channel to measure the resistance of the thermistor. In the image below the channel is called Resistance:
A Calculated Channel must be created in order to apply the Steinhart-Hart equation to the resistance data to convert it to valid temperature data. This is done by selecting a User Defined formula within the Formula Settings. The Steinhart-Equation should then be entered in the User defined formula field. In the figure below the equation has been entered with 1, 2 and 3 as the a, b and c coefficients, respectively. The formula also refers to the Resistance virtual channel created in the previous step. The remaining settings will be dependent on the thermistor properties and should be filled out according to specifications provided with the sensor:
The Calculated Temperature channel we just created should look similar to the figure below:
With this conversion in place, data from the thermistor is converted to temperature data when the VI Logger Task runs. Related Links: NI 435x User Manual NI Developer Zone: Thermistor Fundamentals NI Developer Zone: Measuring Temperature with an RTD or Thermistor Attachments:     
Report Date: 02/17/2006 Last Updated: 04/20/2009 Document ID: 3UGAOI9N |
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