Abstract: In an aspect, an electromechanical apparatus is provided, comprising an electromagnet, a magnetically permeable rotor, a drive, a current source, a current sensor and processing logic. The electromagnet includes a magnetically permeable housing and a wire coil disposed therein. The rotor spins and is disposed in the path of a magnetic circuit generated by the electromagnet. The drive rotates the rotor relative to the electromagnet housing. The rotor and electromagnet housing vary the reluctance therebetween as the rotor rotates. The current source applies a current to the electromagnet coil, wherein, during rotation of the rotor, fluctuations in the current result in the electromagnet coil due to the aforementioned varying reluctance are superimposed on the applied current. The current sensor senses fluctuations in current in the electromagnet coil. The processing logic reads the sensed current and determines the frequency of the fluctuations, which are correlated to rotor speed.

Abstract: In an aspect, an electromechanical apparatus is provided, comprising an electromagnet, a magnetically permeable rotor, a drive, a current source, a current sensor and processing logic. The electromagnet includes a magnetically permeable housing and a wire coil disposed therein. The rotor spins and is disposed in the path of a magnetic circuit generated by the electromagnet. The drive rotates the rotor relative to the electromagnet housing. The rotor and electromagnet housing vary the reluctance therebetween as the rotor rotates. The current source applies a current to the electromagnet coil, wherein, during rotation of the rotor, fluctuations in the current result in the electromagnet coil due to the aforementioned varying reluctance are superimposed on the applied current. The current sensor senses fluctuations in current in the electromagnet coil. The processing logic reads the sensed current and determines the frequency of the fluctuations, which are correlated to rotor speed.