Bridge circuit

A bridge circuit has two parallel branches joined by a cross-connection. It is commonly used to measure an unknown impedance or convert electrical power.

Wheatstone bridge: A four-resistor bridge whose balance condition determines an unknown resistance. Its null-balance method is the classic example of bridge measurement.
Kelvin bridge: A bridge circuit designed to measure very low resistances while reducing lead and contact resistance errors. Its extra connections adapt bridge measurement to tiny resistances.
Kirchhoff's circuit laws: Rules stating that currents and voltages are conserved at circuit nodes and around closed loops. They provide the equations used to derive bridge balance.
Wien bridge: An AC bridge using resistors and capacitors to compare frequency-dependent impedances. Its frequency-sensitive balance supports oscillator design rather than only component measurement.
Bridge balance: The condition in a bridge network where the cross-connection carries no current or voltage difference. At balance, known arm values determine the unknown impedance.
Maxwell bridge: An AC bridge that measures an unknown inductance using a standard capacitor and resistors. It extends bridge balance to inductance measurement.
Voltage divider: A series-resistor network that produces an output voltage proportional to its resistance ratio. Each side of a resistive bridge acts as a voltage divider.
Hay bridge: An AC bridge suited to measuring inductors with high quality factors. It is preferred over the Maxwell bridge for high-Q inductors.
Impedance: The frequency-dependent opposition that a circuit presents to alternating current. AC bridge balance compares complex impedances rather than only resistances.
Schering bridge: An AC bridge used to measure capacitance and dielectric loss. It uses balance to characterize insulating materials and capacitors.

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