Strain gauge connections and Bridge Circuits
How to wire a strain gauge depends on the type of instrument. See the table below for combinations of measurement method and bridge circuit.
| Measuring mode example |
Bridge circuit | Wiring connection to Switching Box |
Wiring connection to Bridge Box |
Bridge Output |
|---|---|---|---|---|
Quarter bridge |
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E : Input voltage e : Output voltage ⊿e : Output voltage due to strain e0 : Output voltage before strain occurrence R0 : Resistance before strain occurrence ⊿R : Resistance change due to strain ε : Strain amount K : Gauge Factor of strain gauge e = e0＋⊿e R1 = R0＋⊿R R = R0  |
Quarter bridge 3-wire Compensates change 
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Quarter bridge 3-wire width two gauges 
|
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R1 = R0＋⊿R R2 = R0＋⊿R R = 2R0 
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Quarter bridge width four gauges 
|
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R1 = R2 = R3 = R4 = R0＋⊿R R = R0  |
Half bridge width 1-active and 1-dummy gauge
|
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R1 = R0＋⊿R R2 = R0 = R 
|
Half bridge width two active gauges |
R1 ＝R0＋⊿R R2 ＝R0－ν⊿R  ν : Poisson's ratio |
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Half bridge width 2 active gauges : Bending strain
|
R1 = R0＋⊿R R2 = R0ー⊿R R = R0 
|
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Half bridge common dummy
Sharing to 
|
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Only for switching box | R1 = R0＋⊿R R2 = R0 = R 
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Opposite arm Half bridge with 2 active gauges 
|
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Only for bridge box Accommodated models SB-120B SB-128A SB-123A |
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R1 = R0＋⊿R R2 = R0＋⊿R R = R0 
|
| Opposite arm Half bridge with 3-wire 2 active gauges 
|
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Only for bridge box Accommodated models SB-120B SB-128A SB-123A |
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R1 = R0＋⊿R R2 = R0＋⊿R R = R0 
|
| Full bridge width 4 active gauges : Uniaxial strain 
|
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R1 = R3＝R0＋⊿R R2 = R4＝R0－v・⊿R  ν : Poisson's ratio |
| Full bridge width 4 active gauges : Bending strain 
|
R1 = R3＝R0＋⊿R R2 = R4＝R0ー⊿R ⊿e = EKε |
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| Full bridge width 4 active gauges : Torque 
|
R1 = R3＝R0＋⊿R R2 = R4＝R0ー⊿R ⊿e = EKε |
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| Full bridge width 2 active and 2 dummy gauges 
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R1 = R3＝R0＋⊿R R2 = R4＝ R R = R0 
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Output voltage due to strain is based on the condition that output voltage before strain generation(e0) is zero.