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Datasheets and User Guides

Software & Driver


14.1.3 RTD [T-Series Datasheet]


AIN#_EF_INDEX values:

40: PT100
41: PT500
42: PT1000

This RTD Extended Feature automatically performs calculations for a Resistance Temperature Detector (RTD). RTD types are listed above.

When AIN#_EF_READ_A is read, the T-series device reads an analog input and calculates the resistance of the RTD. Temperature is then calculated using the rational polynomial technique.

An RTD (aka PT100, PT1000) is a type of temperature sensor.  See the Temperature Sensors App Note.

An RTD provides a varying resistance, but the LabJack measures voltage, so some sort of circuit must be used to convert the varying resistance to a varying voltage.  This AIN-EF supports various excitation circuits, the best and easiest is usually the LJTick-Resistance, which would be excitation circuit #4.


To configure, write to the following registers.

AIN#_EF_CONFIG_A - Options: Selects temperature units:

  • 0 = K
  • 1 = °C
  • 2 = °F

AIN#_EF_CONFIG_B - Excitation Circuit Index: Specifies which excitation circuit is used.

See Excitation Circuits for circuit options.

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

AIN#_EF_CONFIG_D - Excitation Volts or Amps: The number of volts or amps provided as the excitation circuit voltage source or current source.

AIN#_EF_CONFIG_E - Excitation OhmsThe resistance in ohms of the shunt resistor.


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


For results, read the following registers.

AIN#_EF_READ_A: Final calculated temperature.
AIN#_EF_READ_B: Resistance of the RTD.
AIN#_EF_READ_C: Voltage across the RTD.
AIN#_EF_READ_D: Current through the RTD.

Only reading AIN#_EF_READ_A triggers a new measurement.


Shunt resistance, circuit #3:

To configure AIN0 to use the shunt resistor circuit with shunt resistor value = 2700 Ω and RTD type 100:

AIN0_EF_INDEX = 40       // Set AIN_EF0 to RTD100.
AIN0_EF_CONFIG_A = 0     // Set result units to kelvin. 
AIN0_EF_CONFIG_B = 3     // Set excitation circuit to 3.
AIN0_EF_CONFIG_C = 1     // Set the second AIN to AIN1.
AIN0_EF_CONFIG_E = 2700  // Set the shunt resistance.

Now each read of AIN0_EF_READ_A will measure the voltages on AIN0 and AIN1 and return the calculated temperature.