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Software & Driver

 

14.1.5 Thermistor

*BETA*

Index: 50 

AIN Extended Feature Thermistor computes the temperature of a thermistor-type temperature sensor.

Operation:

Reading from the AIN#_EF_READ_A register begins the conversion process. The T7 will measure the voltage on the AIN and compute temperature using the Steinhart-Hart equation. The temperature, measured voltage and calculated resistance are then available to be read from the result registers.

Configuration:

Both the Thermistor's Steinhart-Hart constants and information about the excitation circuit need to be provided. Information about the excitation circuits can be found in section 14.1.0.1. Steinhart-Hart constants are normally provided in the thermistor's datasheet.

Configuration Registers: 

CONFIG_A: Thermistor Options - Requires firmware 1.0221. Selects temperature units. 0 = K, 1 = C, 2 = F. 
CONFIG_B: Excitation Type
CONFIG_C: Second AIN
CONFIG_D: Excitation Detail Volts / Amps
CONFIG_E: Excitation Detail Ohms
CONFIG_F: R25
CONFIG_G: Steinhart-Hart A
CONFIG_H: Steinhart-Hart B
CONFIG_I: Steinhart-Hart C
CONFIG_J: Steinhart-Hart D

Result Registers:

READ_A: Thermistor Temperature
READ_B: Thermistor Resistance
READ_C: Thermistor Voltage

Example:

In this example we will configure a T7 to read from a Vishay NTCLE100E3103HT1 Thermistor using a LabJack LJTick-Resistance to complete the excitation circuit.  The LJTick-Resistance is connected to the AIN0-1 terminal block. The thermistor is connected between the Vref and INA terminals on the LJTick-Resistance.

  • AIN0_EF_INDEX = 50
  • AIN0_EF_CONFIG_A = 0 -- No options, will output results in degrees Kelvin.
  • AIN0_EF_CONFIG_B = 4 -- Excitation circuit #4.
  • AIN0_EF_CONFIG_C = 0 -- Second AIN, not used for excitation circuit #4.
  • AIN0_EF_CONFIG_D = 2.5 -- 2.5 V provided by the LJTick-Resistance
  • AIN0_EF_CONFIG_E = 1000 -- 1 kΩ shunt resistor provided by the LJTick-Resistance.
  • AIN0_EF_CONFIG_F = 10000 -- R25 The nominal resistance of the thermistor at 25 ºC.
  • AIN0_EF_CONFIG_G = 0.003354016 -- Constants from the thermistor's datasheet.
  • AIN0_EF_CONFIG_H = 0.000256985
  • AIN0_EF_CONFIG_I = 0.000002620
  • AIN0_EF_CONFIG_J = 0.000000064

AIN0 settings such as resolution, range, settling, and differential may need to be configured before continuing.

Results:

  • Read_A = 296.47 -- Temperature of the thermistor. (K)
  • Read_B = 10768 -- Calculated resistance. (Ω)
  • Read_C = 2.288 -- Voltage across the thermistor. (V)