The article presents the microprocessor device for predictive maintenance systems for electrical machines, the principle of operation of which is based on measuring the quality factor of windings. It is proposed to use the quality factor as an informative parameter for diagnosing the winding condition, in particular, detecting short-circuited coils. Complete and simplified equivalent winding diagrams were constructed, and analytical expressions for the quality factor were obtained, taking into account losses in the magnetic core and insulation. The method for determining the quality factor based on the phase shift between voltages has been developed, which is implemented in the form of a structural diagram of a sensor with a microcontroller. Simulations were conducted that confirmed the high sensitivity of the quality factor to the number of short-circuited coils, unlike inductance. The proposed approach allows for accurate diagnostics of windings as part of predictive maintenance systems, meeting the requirements of digitalization of industrial processes.