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14.1.5 Thermistor [T-Series Datasheet]

Overview

AIN#_EF_INDEX values:

50: calculate temperature using the Steinhart-Hart equation
51: calculate temperature using the beta equation

This Thermistor Extended Feature automatically performs the necessary calculations for thermistors using the Steinhart-Hart equation or the beta equation.

Steinhart-Hart vs. beta: The beta function works well over a limited range of about 50 ºC. Typical error is ~±0.5 ºC. The Steinhart-Hart is usually more accurate than ±0.01 ºC across a larger range.

Configuration

To configure, write to the following registers.

AIN#_EF_CONFIG_A - Thermistor Options: Selects temperature units:

  • 0 = K
  • 1 = °C
  • 2 = °F

AIN#_EF_CONFIG_B - Excitation Circuit Index: The index of the voltage divider excitation circuit to be used

See 14.1.0.1 Excitation Circuits for circuit indices.

AIN#_EF_CONFIG_C - Excitation AIN Channel Number: The AIN channel number of the AIN line used to measure the RTD's excitation.

Ignored if the Excitation Circuit Index does not use a second AIN.

AIN#_EF_CONFIG_D - Excitation Detail Volts: The number of volts provided as the excitation circuit voltage source.

AIN#_EF_CONFIG_E - Excitation Detail Ohms: The resistance in ohms of the shunt resistor.

AIN#_EF_CONFIG_F - R25 Ohms: The nominal resistance in ohms of the thermistor at 25 °C.

Steinhart-Hart Beta
AIN#_EF_CONFIG_G A constant ß
AIN#_EF_CONFIG_H B constant ºC at which ß was calculated
AIN#_EF_CONFIG_I C constant No meaning
AIN#_EF_CONFIG_J D constant No meaning
 

The G, H, I, and J config registers have different meaning for Steinhart-Hart and beta. Steinhart-Hart constants are normally provided in the thermistor's datasheet or obtained from the manufacturer.

Remarks

The normal analog input settings are used for negative channel, resolution index, settling, and range.

T7 only: If voltage will stay below 1.0V, use the 1.0V range for improved resolution and accuracy.

Results

For results, read the following registers.

AIN#_EF_READ_A: Thermistor Temperature
AIN#_EF_READ_B: Thermistor Resistance
AIN#_EF_READ_C: Thermistor Voltage

Only reading AIN#_EF_READ_A triggers a new measurement.

Example

This example configures a LabJack to read from a Vishay NTCLE100E3103 10k 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                -- Steinhart-Hart
AIN0_EF_CONFIG_A = 1              -- Output degrees Celsius.
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 = 10000          -- 10 kΩ shunt resistor provided by the LJTick-Resistance-10k.
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 = 0.00000006383

Results:

AIN0_EF_READ_A = 23.19    -- Temperature of the thermistor. (°C)
AIN0_EF_READ_B = 10829.4  -- Calculated resistance. (Ω)
AIN0_EF_READ_C = 1.299774 -- Voltage across the thermistor. (V)

Overview

AIN#_EF_INDEX values:

50: calculate temperature using the Steinhart-Hart equation
51: calculate temperature using the beta equation

This Thermistor Extended Feature automatically performs the necessary calculations for thermistors using the Steinhart-Hart equation or the beta equation.

Steinhart-Hart vs. beta: The beta function works well over a limited range of about 50 ºC. Typical error is ~±0.5 ºC. The Steinhart-Hart is usually more accurate than ±0.01 ºC across a larger range.

Configuration

To configure, write to the following registers.

AIN#_EF_CONFIG_A - Thermistor Options: Selects temperature units:

  • 0 = K
  • 1 = °C
  • 2 = °F

AIN#_EF_CONFIG_B - Excitation Circuit Index: The index of the voltage divider excitation circuit to be used

See 14.1.0.1 Excitation Circuits for circuit indices.

AIN#_EF_CONFIG_C - Excitation AIN Channel Number: The AIN channel number of the AIN line used to measure the RTD's excitation.

Ignored if the Excitation Circuit Index does not use a second AIN.

AIN#_EF_CONFIG_D - Excitation Detail Volts: The number of volts provided as the excitation circuit voltage source.

AIN#_EF_CONFIG_E - Excitation Detail Ohms: The resistance in ohms of the shunt resistor.

AIN#_EF_CONFIG_F - R25 Ohms: The nominal resistance in ohms of the thermistor at 25 °C.

Steinhart-Hart Beta
AIN#_EF_CONFIG_G A constant ß
AIN#_EF_CONFIG_H B constant ºC at which ß was calculated
AIN#_EF_CONFIG_I C constant No meaning
AIN#_EF_CONFIG_J D constant No meaning
 

The G, H, I, and J config registers have different meaning for Steinhart-Hart and beta. Steinhart-Hart constants are normally provided in the thermistor's datasheet or obtained from the manufacturer.

Remarks

The normal analog input settings are used for negative channel, resolution index, settling, and range.

T7 only: If voltage will stay below 1.0V, use the 1.0V range for improved resolution and accuracy.

Results

For results, read the following registers.

AIN#_EF_READ_A: Thermistor Temperature
AIN#_EF_READ_B: Thermistor Resistance
AIN#_EF_READ_C: Thermistor Voltage

Only reading AIN#_EF_READ_A triggers a new measurement.

Example

This example configures a LabJack to read from a Vishay NTCLE100E3103 10k 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                -- Steinhart-Hart
AIN0_EF_CONFIG_A = 1              -- Output degrees Celsius.
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 = 10000          -- 10 kΩ shunt resistor provided by the LJTick-Resistance-10k.
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 = 0.00000006383

Results:

AIN0_EF_READ_A = 23.19    -- Temperature of the thermistor. (°C)
AIN0_EF_READ_B = 10829.4  -- Calculated resistance. (Ω)
AIN0_EF_READ_C = 1.299774 -- Voltage across the thermistor. (V)