How to Assemble a Strain Gauge Bridge Circuit

Bridge circuits refer to electric circuits configured to link four elements in a bridge-like manner, and typical types include Wheatstone bridges and meter bridges. In a bridge circuit, if the value of each element is balanced, the output voltage is “0” irrespective of the input voltage. Strain gauges use this property to measure strain. The way that the circuit is assembled varies depending on the measurement target, and different circuits are used for different measurement purposes.
This section explains how to assemble a circuit and methods to connect to the strain measurement unit “NR-ST04.”

“Strain gauge”—this beginner’s guide introduces measurement techniques using a strain gauge!

This guide explains strain measurement—from basic knowledge to practical implementation and techniques—in a manner that is easy to understand even for beginners.

Get the PDF for more details

Tensile strain/compressive strain
Bending strain
Twisting strain

Tensile strain/compressive strain

One-gauge method, two-wire system

This is the most common connection method.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1×	-	-

One-gauge method, three-wire system

This method can cancel the temperature effect of the lead wires.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1×	-	✓

One-gauge method (two sheets), two-wire system

Two 60 Ω strain gauge sheets are connected in series. This method can cancel the bending strain.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1×	-	-

One-gauge method (two sheets), three-wire system

Two 60 Ω strain gauge sheets are connected in series. This method can cancel the temperature effect of the lead wires and the bending strain.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1×	-	✓

Two-gauge method, adjacent sides (active/dummy)

A reference strain gauge is attached to a test piece that is not subjected to stress and is made of the same material as the measurement target. The apparent strain that has occurred due to the temperature change is measured by the reference gauge and canceled.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1×	✓	✓

Two-gauge method, adjacent sides (two-active perpendicular arrangement)

One sheet containing two elements (two axes crossed) is attached. Output: (1 + Poisson’s ratio) times

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		1 + ν	✓	✓

Two-gauge method, opposite sides (two actives), two-wire system

Because the NR-ST04’s built-in bridge box does not support the opposite side, an external bridge box or two channels are used for calculation.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2×	-	-	Method 1: Use an external bridge box. Connect the bridge box and the NR-ST04 with the four-gauge method. Method 2: With the one-gauge method, two-wire system, connect two strain gauge sheets, one to CH1 and one to CH2. Calculation: (CH1 + CH2)

Two-gauge method, opposite sides (two actives), three-wire system

Because the NR-ST04’s built-in bridge box does not support the opposite side, an external bridge box or two channels are used for calculation.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2×	-	✓	Method 1: Use an external bridge box. Connect the bridge box and the NR-ST04 with the four-gauge method. Method 2: With the one-gauge method, three-wire system, connect two strain gauge sheets, one to CH1 and one to CH2 Calculation: (CH1 + CH2)

Four-gauge method (active/dummy)

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2×	✓	✓

Four-gauge method (four-active perpendicular arrangement)

Two sheets containing two elements (two axes crossed) are attached. (Four gauges in total) Output: 2 × (1 + Poisson’s ratio) times

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2× (1 + ν)	✓	✓

Download PDF

Bending strain

Two-gauge method, adjacent sides

Strain gauges are attached on the front and the back. This method enables strain measurement without being affected by tensile strain or compressive strain.

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2×	✓	✓

Four-gauge method

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		4×	✓	✓

Download PDF

Twisting strain

Two-gauge method, adjacent sides

Two strain gauge sheets are attached by tilting them ±45° against the axis (for two elements ±45° shear).

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		2×	✓	✓

Four-gauge method

Measurement example	Bridge circuit	Output	Temperature compensation	Lead wire temperature compensation	Wiring to the NR-ST04
		4×	✓	✓

Download PDF

Scaling

To obtain 0.5 times through scaling, configure the settings as shown above.

INDEX

For those who want to learn
more about strain!

This guide summarizes the basics, practical implementation, and techniques of strain measurement!

Download