The Wheatstone Bridge was originally developed by Charles Wheatstone to measure unknown resistance values and measuring instruments, voltmeters, ammeters, etc. Although today digital multimeters provide the simplest way to measure a resistance, The Wheatstone Bridge can still be used to measure very low values of resistances down in the milli-Ohms range. A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of abridge circuit, one leg of which includes the unknown component. The primary benefit of a wheatstone bridge is its ability to provide extremely accurate measurements .
is the unknown resistance to be measured; R1,R2 and R3 are resistors of known resistance and the resistance of R2 is adjustable. If the ratio of the two resistances in the known leg (R2/R1) is equal to the ratio of the two in the unknown leg (Rx/R3), then the voltage between the two midpoints (B and D) will be zero and nocurrent will flow through the galvanometer (Vg). If the bridge is unbalanced, the direction of the current indicates whether R2 is too high or too low. R2 is varied until there is no current through the galvanometer, which then reads zero.