What is a AC Potentiometer ?
AC Potentiometer Definition
An AC potentiometer measures unknown voltage by balancing it with a known voltage, including both magnitude and phase.
Types of AC Potentiometers
Polar type
Coordinate type
Polar Type Potentiometer
Measures magnitude and phase angle using separate scales and components like a phase-shifting transformer.

Coordinate Type Potentiometer
Measures in-phase and quadrature components of the unknown voltage using two potentiometers in one circuit.

Applications
Measurement of self-inductance
Calibration of voltmeter
Calibration of Ammeter
Calibration of watt meter