Metal resistance strain gauge bridge circuit diagram

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When the metal resistance strain gauge is applied to the mechanical measurement, it needs to be used together with the bridge circuit. Since the output signal of the strain gauge bridge circuit is weak, the DC amplifier is prone to zero drift phenomenon, so the AC amplifier is used to amplify the signal. Therefore, the strain gauge bridge circuit is generally powered by alternating current to form an alternating current bridge. According to different reading methods, the bridge is divided into two types: balanced bridge and unbalanced bridge. Balanced bridges are only suitable for measuring static parameters, while unbalanced bridges are suitable for measuring dynamic parameters.

Since the DC bridge and the AC bridge are similar in the work, for the sake of convenience, only the DC unbalanced bridge will be introduced below.

The circuit shown is the circuit that outputs the DC unbalanced bridge of the terminating amplifier. The first bridge arm is connected to the resistance strain gauge R1, and the other three bridge arms are connected to the fixed resistor. When strain occurs at the end of the strain gauge R1, since there is no resistance change, the bridge maintains R1.R4=R2.R3 of the initial equilibrium condition, and thus the output is zero, that is,

UOUT=A(Rl.R4 - R2.R3)=0

When the strain gauge is strained, the strain gauge produces a resistance change of ΔR1, and the bridge is in an unbalanced state.

Hypothesis And taking into account the initial balance conditions of the bridge , omit the trace amount in the denominator , the above formula can be written as

It can be seen from the equation that the output voltage is proportional to the amount of change in resistance generated when the strain gauge is strained.