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App Notes

Software & Driver

 

14.1.6 Resistance [T-Series Datasheet]

Overview

AIN#_EF_INDEX: 4

This Resistance Extended Feature will calculate the resistance of a given circuit element.

Configuration

To configure, write to the following registers.

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.

Remarks

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

Results

For results, read the following registers.

AIN#_EF_READ_A: Resistance
AIN#_EF_READ_B: Voltage
AIN#_EF_READ_C: Current

Only reading AIN#_EF_READ_A triggers a new measurement.

Example

An unknown resistor to be measured (a 10 kΩ resistor is used in this test) is connected in series with a 200 µA current source.

AIN0_EF_INDEX = 4
AIN0_EF_CONFIG_B = 0   -- Excitation circuit 0 (200 µA current source)

Reading results:

  • AIN0_EF_READ_A returns 10089.7 Ω
  • AIN0_EF_READ_B returns 2.012 V
  • AIN0_EF_READ_C returns 199 µA