Remotely Sensing Optical Tachometer.
OFFICE OF THE SECRETARY OF THE ARMY WASHINGTON D C
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The invention relates to a remotely sensing optical tachometer for measuring the spin rate of a rotating member. The invention provides a simple optical system for measuring the spin andor rate of change of spin, of, for example, an artillery shell or test projectile. The system provides a real-time readout of the spin rate, and requires no instrumentation aboard the projectile except for a small plane mirror that is attached obliquely to one end of the spinning projectile. The system directs a collimated beam of light that is reflected off the plane mirror back into the system where it traverses a stationary reticle that has alternating transparent and opaque sectors thereon. The frequency with which the light passes through the transparent portions of the reticle provides a direct indication of the spin rate of the rotating member.