Kelvin bridge

Kelvin bridge

A specialized version of the Wheatstone bridge network designed to eliminate, or greatly reduce, the effect of lead and contact resistance and thus permit accurate measurement of low resistance. The circuit shown in the illustration accomplishes this by effectively placing relatively high-resistance-ratio arms in series with the potential leads and contacts of the low-resistance standards and the unknown resistance. In this circuit R_A and R_B are the main ratio resistors, R_a and R_b the auxiliary ratio, R_x the unknown, R_s the standard, and R_y a heavy copper yoke of low resistance connected between the unknown and standard resistors.

A Kelvin bridge used to measure an unknown low resistance

As with the Wheatstone bridge, the Kelvin bridge for routine engineering measurements is constructed using both adjustable-ratio arms and adjustable standards. However, the ratio is usually continuously adjustable, over a short span, and the standard is adjustable in appropriate steps to cover the required range. See Bridge circuit, Resistance measurement, Wheatstone bridge

Kelvin bridge