6

Developing Strain Gauges and Instruments

STRAIN GAUGE BRIDGE

Strain gauge connections and bridge circuitsConnection diagram varies according to strainmeter type.

Output voltage due to strain is based on the condition that output voltage before strain generation(e0) is zero.

Measuring mode Bridge circuit Bridge outputOn bridge boxOn switching box

Quarter bridge

Quarter bridge with 3-wiresystem

Quarter bridge with 4 gauges

Full bridge

Full bridge

Half bridge with 1-active and1-dummy gauges

Half bridge with 2-active gaugeseliminating tensile strain

Quarter bridge with doublegauge and 3-wire systemeliminating bending strain

R1R

R R

E

e

R1R

R R

E

e

R2

R1R

R R

E

e

R2

R3R4

R1

R R

E

e

R2

R1e

E

R4

R3

R2

5 6 7 8

1 2 3 4

5 6 7 8

1 2 3 4

5 6 7 8

1 2 3 4

5 6 7 8

1 2 3 4

5 6 7 8

1 2 3 4

5 6 7 8

1 2 3 4

R1

R1

R1 R2

R1 R2

R3 R4

R1 R2

R1 R2

R3R4

60Ωeach

R1

R1

R1

R2

R1

R3

R4

R2

R1

R2

R1

R2

R2 R1 R4

R3

R2R1R3R4

R1R

R R

E

e

R1R2

R3 R4

ABCDE

R1

ABCDE

R2

R2

ABCDE

R1

R4 R3

ABCDE

R2 R1

ABCDE

R1

ABCDE

R1 :Exciting voltage:Output voltage

:Strain:Gauge Factor

:Output voltage due to strain:Output voltage before strain generation:Resistance before strain generation:Resistance change due to strain