This bridge is formed by resistors and used to resistance measurements. The circuit of a Wheatstone Bridge is shown in figure bellow. The detecting device can be a galvanometer. The applied signal is a DC voltage.
Note: When used to resistance measurements, one of the resistance is unknow (R4 = Rx for instance) and other is variable to balance the bridge (R3 for instance).
The Wheatstone also operates with an AC signal source replacing the indicator for a convenient one.
Formula
When balanced:
R4 = ( R1 / R2 ) x R3
Where: R1, R2, R3, R4 are the resistances in the arms of the bridge in ohm (Ω)
Application example:
What is the value of R4 in the bridge shown in figure 118, when the balance condition is found with R1 = 100 Ω, R2 =200 Ω and R3 = 300 Ω?
Data:
R1 = 100 Ω
R2 = 200 Ω
R3 = 300 Ω
R4 = ?
Using the formula:
R4 = (100 / 200 ) x 300
R4 = 150 Ω
