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Datasheets and User Guides

App Notes

Software & Driver

 

14.1.3 RTD

Overview

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.

Configuration

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 14.1.0.1 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.

Remarks

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

Result

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.

Example

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.