Bridge Configurations

This topic explains some common bridge configurations used in strain measurements.

NI-DAQmx strain virtual channels use the following equation to scale voltage readings to strain units.

Vr = (VCH / VEX)STRAINED – (VCH / VEX)UNSTRAINED

where VEX is the excitation voltage, and VCH is the measured voltage.

Quarter-Bridge Type I

The following figure shows how to position a strain gage resistor in an axial configuration for the quarter-bridge type I.

The following figure shows how to position a strain gage resistor in a bending configuration for the quarter-bridge type I.

Quarter-bridge type I strain gage configurations have the following characteristics:

Quarter-Bridge Type I Circuit Diagram

The following symbols apply to the circuit diagram:

To convert voltage readings to strain units for quarter-bridge configurations, use the following equation.

where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, RL is the lead resistance, and Rg is the nominal gage resistance.

Quarter-Bridge Type II

The following figure shows how to position a strain gage resistor in an axial configuration for the quarter-bridge type II.

The following figure shows how to position a strain gage resistor in a bending configuration for the quarter-bridge type II.

Quarter-bridge type II strain gage configurations have the following characteristics:

Quarter-Bridge Type II Circuit Diagram

The following symbols apply to the circuit diagram:

Half-Bridge Type I

The following figure shows how to position strain gage resistors in an axial configuration for the half-bridge type I.

The following figure shows how to position strain gage resistors in a bending configuration for the half-bridge type I.

Half-bridge type I strain gage configurations have the following characteristics:

Half-Bridge Type I Circuit Diagram

The following symbols apply to the circuit diagram:

To convert voltage readings to strain units, use the following equation.

where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, v is the Poisson's ratio, RL is the lead resistance, and Rg is the nominal gage resistance.

Half-Bridge Type II

The half-bridge type II configuration only measures bending strain.

The following figure shows how to position strain gage resistors in a bending configuration for the half-bridge type II.

Half-bridge type II strain gage configurations have the following characteristics:

Half-Bridge Type II Circuit Diagram

The following symbols apply to the circuit diagram:

To convert voltage readings to strain units, use the following equation.

where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, RL is the lead resistance, and Rg is the nominal gage resistance.

Full-Bridge Type I

The full-bridge type I configuration only measures the bending strain.

The following figure shows how to position strain gage resistors in a bending configuration for the full-bridge type I.

Full-bridge type I strain gage configurations have the following characteristics:

Full-Bridge Type I Circuit Diagram

The following symbols apply to the circuit diagram:

To convert voltage readings to strain units use the following equation.

where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, and GF is the gage factor.

Full-Bridge Type II

The full-bridge type II configuration only measures bending strain.

The following figure shows how to position strain gage elements in a bending configuration for the full-bridge type II.

Full-bridge type II strain gage configurations have the following characteristics:

Full-Bridge Type II Circuit Diagram

The following symbols apply to the circuit diagram:

To convert voltage readings to strain units, use the following equation.

where Vr is the voltage ratio that virtual channels use in the voltage-to-strain conversion equation, GF is the gage factor, and v is the Poisson's ratio.

Full-Bridge Type III

The following figure shows how to position strain gage resistors in an axial configuration for the full-bridge type III.

The full-bridge type III configuration only measures the axial configuration.

Full-bridge type III strain gage configurations have the following characteristics:

Full-Bridge Type III Circuit Diagram

The following symbols apply to the circuit diagram: