1. Use the DAQ_TTR Meas Initialize VI to initialize hardware and create DAQmx Tasks for temperature thermistor measurement.
2. Pass the temperature thermistor measurement DAQmx Task to the DAQ_TTR Meas Configure and Measure VI.
3. Configure the DAQ_TTR Meas Configure and Measure VI.
   Note For more accurate measurements, you can use NI MAX to calibrate any global channels specified in the Initialize VI.

   • Execution Settings—By default, the Configure and Measure VI also executes the measurement. If you are using a trigger for your measurement, choose the Configure Only or Measure Only execution option to avoid automatic execution.

     Configuration Settings—Configure the range and terminal settings. Global settings are applied to any channel without channel-specific settings. Use the Specific Channel Settings to configure a channel, including physical analog input temperature channels.

     Note Current excitation is not supported. The Temperature Thermistor measurement library supports only external voltage excitation.

     Note The Temperature Thermistor measurement library provides A B C parameter and Beta parameter support. Refer to the Measurement Details section for more information.

     Configure the timing related parameters for temperature measurement. The Timing setting configures sample clock source input, sampling rate, number of samples, and the sample timing engine used for the DAQmx Task.

     • Acquisition Time = Number of Samples/Sample Rate
     • Specify Auto to automatically select the timing engine.

     Note For NI 63xx (X Series) and other DAQ devices, use Auto mode only. The sample timing engine is only used for cDAQ and TestScale platforms, which support multiple timing engines.

     Note Timing engine configurations are identical for the TestScale and cDAQ chassis. Refer to cDAQ-91xx and TestScale Chassis Timing Engines for more information.

     Note Refer to the relevant specifications document to identify the maximum sampling rate for your device. Values that exceed the maximum sampling rate generate errors.

     Configure triggers to start the source or measurement based on various trigger events. Trigger options include no trigger or digital start triggers.

     Output Data—The VI outputs the following data.

     Temperature Waveforms—Displays the captured temperature waveforms.

     Temperature Measurements—Provides the derived post-analyzed data from the captured temperature waveforms, which is output as an averaged temperature represented in degrees Celsius or degrees Kelvin.

     Acquisition Time—Calculated acquisition time for the measurement.

4. Wire the updated temperature thermistor measurement task from DAQmx Task Out.
5. Close the temperature thermistor measurement task using DAQ_TTR Meas Close VI.

Execution Option Settings

Configure and Measure—Configures the instrument and executes the measurement.

Configure Only—Sets the configuration of the instrument but does not fetch data and execute the measurement. Use this option when a channel is configured to wait for a trigger based on a software or hardware event. This operation should be followed by a Measure Only operation.

Measure Only—Skips configuration to fetch the data captured by the instrument, process the data, and return the measurements. A Configure Only operation is required to initiate each measurement task. Any DAQ Measure Only operation, including repeated operations, must be preceded by a DAQ Configure Only operation.

Best Practices

• For faster measurements, set the maximum sampling rate possible for the given Sample Clock Source input and assign a smaller Number of Samples to capture.
• For better resolution, increase the number of samples (for example, 1000 samples).

• You can use any other external source for voltage excitation in thermistor measurements.
• Use a remote sensing method with power supply modules for more reliable voltage excitation values.

Measurement Details

The Temperature Thermistor measurement library derives temperature measurements from thermistor parameters using the following methods. A B C parameter-based temperature measurements provides more accurate results than beta parameter-based measurements because the beta parameter calculation effectively substitutes zero for the C parameter during Steinhart-Hart equation conversion.

A B C Type —Specifies the Steinhart-Hart equation parameters used to perform temperature measurements. For the A, B and C parameters, refer to the thermistor datasheet. The following Steinhart-Hart equation illustrates how the parameters are applied.

$\frac{1}{T}=A+B\left(\ln R\right)+C {(\ln R)}^3$

Where
T = temperature in degrees Kelvin
R = measured thermistor resistance in Ohms
A, B, C = constants provided by the thermistor manufacturer

Beta Parameter Type—Characterized with the β (beta) parameter equation which is, essentially, a Steinhart-Hart equation where the A, B and C constants are replaced with β, T₀ and R₀, as shown in the following example:

$A=\frac{1}{T_0}-\left(\frac{1}{\beta }\right)\ln R_0$

$B= \frac{1}{\beta }$

$C=0$

Substituting these values in a Steinhart-Hart equation gives the following beta parameter equation: