A resolver is best described as which of the following?

• A. A sensor for measuring airflow
• B. A device to measure humidity
• C. A device for converting AC to DC
• D. A revolving transformer used to measure the degrees of rotation in a motor

Answer: (D)

A resolver is a revolving transformer used to measure angular position. When the rotor (the rotating part) turns, the magnetic coupling between the rotor and the stator windings creates voltages on two stator windings that vary with the rotation angle. With AC excitation on the primary, those two secondary signals are proportional to sine and cosine of the angle, giving a precise indication of the shaft’s position. This makes resolvers ideal for providing continuous angular position feedback in motors and servo systems.

It isn’t used to measure environmental conditions like airflow or humidity, and it isn’t a device that converts AC to DC. Those functions are served by other sensors and by rectifiers, respectively.