What is hay bridge?

Hay bridge is a type of bridge circuit used for measuring the impedance of an unknown circuit element. The circuit consists of a four-arm bridge network where two arms contain resistors of known value, one arm contains a known capacitor, and the other arm contains the unknown impedance. The circuit is balanced by varying the value of a variable resistor until no current passes through the detector circuit. The unknown impedance can be calculated using the values of the resistors and known capacitor in the bridge circuit. The bridge circuit is named after American electrical engineer Edward Hay. It is widely used in electrical and electronic laboratories for measuring the impedance of different types of electronic components and circuits. Hay bridge is a high accuracy measuring technique and is commonly used in audio frequency (AF) signal analysis.