Wheatstone Bridge Calculator - Calculation Formulas
The Wheatstone bridge is a very useful circuit. When the bridge is perfectly balanced, with the right resistance being the same as the left resistance (R1=R3, and R2=Rx), the voltage across the bridge is zero. However, due to a small change in resistance, the bridge becomes unbalanced and a voltage difference appears. Wheatstone bridges are used in a variety of devices such as strain gauges, pressure gauges, sensors, etc.
The bridge voltage is calculated as follows：
VB= Vin*[Rx/(R3+Rx)- R2/(R1+R2)]
If R3=R1, 和 Rx= R2+delta, Then
VB= Vin*[ (R2+delta)/(R1+R2+delta)-R2/(R1+R2)]
Now, if we assume that delta is smaller than R1 + R2, then
VB= ~ Vin*[delta/(R1+R2)]
So we can see that the bridge voltage is approximately proportional to the error delta, divided by the sum of the resistors on one side.
Given the bridge voltage, we can calculate the value of an unknown resistor.
(R1+R2)*(R3+Rx)*VB/Vin= Rx*(R1+R2)+ R2*(R3+Rx)
Rx*(R1+R2)*VB/Vin + R3* (R1+R2)VB/Vin= Rx*R1+Rx*R2 - R2*R3- Rx*R2
Rx*R1 - Rx*(R1+R2)*VB/Vin = R2*R3 + R3* (R1+R2)VB/Vin
Rx = (R2*R3 + R3* (R1+R2)VB/Vin )/ (R1- (R1+R2)*VB/Vin)