Sensing rotational speed by amplitude modulating a continuous microwave signal

Claim 1

A rotating member speed sensor comprising, in combination, microwave reflecting disc means connected to the rotating member for rotation therewith, the disc means having a series of grooves spaced around the periphery thereof, the grooves being filled with a microwave transparent material for preventing foreign matter buildup therein; microwave-generating means located adjacent to the disc for transmitting a continuous microwave signal toward the periphery of the disc so as to be reflected therefrom; microwave-detecing means located adjacent to the disc for detecting the reflected microwave signal, the detected microwave signal having an amplitude which varies in an inverse relationship to the distance the microwave signal travels between the microwave-generating means and the periphery and between the periphery and the microwave-detecting means, whereby the detected microwave signal is amplitude modulated by the grooves in the periphery of the disc due to the cyclic variation in the distance the microwave signal travels between the microwave-generating means and the periphery and between the periphery and the microwave-detecting means when the disc is rotated, the frequency of the modulation being determined by the number of grooves in the periphery of the disc and the angular velocity of the rotating member; demodulator means for generating an output signal having a frequency equal to the frequency of modulation of the detected microwave signal, the demodulator means including the microwave-detecting means; and indicator means for indicating the angular velocity of the rotating member in response to the frequency of the output signal of the demodulator means.