What is the operation in using kelvin bridge?

The Kelvin double bridge is a type of Wheatstone bridge used for measuring very low resistances. It is more sensitive than a simple Wheatstone bridge, and it can be used to measure resistances down to a few milliohms.

The Kelvin bridge consists of two branches, A and B, which are connected in parallel. The branch A contains the unknown resistance X, and the branch B contains a standard resistor Rs. The bridge is balanced when the potential difference between points C and D is zero.

To balance the bridge, the variable resistor R is adjusted until the galvanometer G reads zero. When the bridge is balanced, the following equation can be used to calculate the unknown resistance X:

X = Rs * (R2 / R1)

Where:

X is the unknown resistance

Rs is the standard resistor

R1 is the resistance in arm 1 of the bridge

R2 is the resistance in arm 2 of the bridge

The Kelvin bridge is a very accurate and sensitive instrument for measuring low resistances. It is often used in the calibration of other electrical instruments and in the testing of electrical components.