Resistance measurements with current excitation

U terminals can be configured to supply precise current excitation for use with resistive bridges. Resistance can be measured by supplying a precise current and measuring the return voltage. The data logger supplies a precise current from terminals configured for current excitation. Return voltage is measured on U terminals configured for single-ended or differential analog input.

U terminals can be configured as current-output terminals under program control for making resistance measurements. For the current return, use the signal ground () terminal closest to the current source terminal. CRBasic instructions that control current excitation include:

  • Resistance() - Applies an excitation current to a circuit and measures the resistance. The maximum excitation current is ±2500 μA.
  • Resistance3W() - Makes a three-wire resistance measurement. The maximum excitation current is ±2500 μA.

Resistive Bridge Circuits with Current Excitation: (use the signal ground () terminal adjacent to the current excitation terminal)

Resistive-bridge type and
circuit diagram		 CRBasic instruction and
fundamental relationship		 Relational formulas

Four Wire

CRBasic Instruction:
Resistance()

Fundamental Relationship1:

  

Four Wire Full Bridge

CRBasic Instruction:
Resistance()

Fundamental Relationship1:

Three Wire

CRBasic Instruction:
Resistance3W()

Fundamental Relationship2:

  

1 Where X = result of the CRBasic bridge measurement instruction with a multiplier of 1 and an offset of 0.

2 Where Ri is the precision internal resistor value that is saved as part of the factory calibration procedure and Rs is the sense resistance.