Apparatus for detecting substantially zero speed of a rotatable device

Claim 1

APPARATUS FOR PROVIDING A SPECIFIC RESPONSE WHEN THE ROTATING SPEED OF A ROTATABLE DEVICE DROPS TO A PREDETERMINED LOW ORDER VALUE RELATIVE TO NORMAL OPERATING SPEED, SAID APPARATUS COMPRISING FIRST AND SECOND ELECTRICAL SPEED FUNCTION SIGNAL GENERATING MEANS EACH FOR PRODUCING IN RESPONSE TO ROTATION OF SAID DEVICE INTERMITTENT ELECTRIC SPEED FUNCTION SIGNALS WHOSE DWELL TIMES INCREASE AS THE ROTATING SPEED OF THE DEVICE DECREASES, AT LEAST ONE OF SAID SIGNAL GENERATING MEANS PRODUCING A SPEED FUNCTION SIGNAL AT ANY GIVEN ANGULAR POSITION OF SAID DEVICE, AN ELECTRIC COMPUTING CIRCUIT COUPLED TO EACH SPEED FUNCTION SIGNAL GENERATING MEANS FOR INTEGRATING THE SPEED FUNCTION SIGNAL OUTPUT OF THE GENERATING MEANS TO PRODUCE A COMPUTED ELECTRIC SIGNAL PROPORTIONAL TO THE INTEGRAL OF THE SPEED FUNCTION SIGNAL OUTPUT OF ITS ASSOCIATED SPEED FUNCTION SIGNAL GENERATOR, EACH OF SAID COMPUTING CIRCUITS HAVING A TIME CONSTANT WHICH IS SO LONG RELATIVE TO THE ROTATION SPEED OF SAID DEVICE THAT SAID COMPUTED SIGNAL CANNOT ATTAIN AT LEAST A PREDETERMINED MINIMUM VALUE WHEN SAID DEVICE IS ROTATING ABOVE SAID LOW ORDER VALUE, SAID TIME CONSTANT BEING SUFFICIENTLY SHORT SO THAT SAID COMPUTED SIGNAL ATTAINS AT LEAST SAID PREDETERMINED MINIMUM VALUE WHEN THE ROTATIONAL SPEED OF SAID DEVICE DROPS TO SAID LOW ORDER VALUE, AND UTILIZATION MEANS COUPLED TO SAID COMPUTING CIRCUITS FOR PROVIDING A SPECIFIC REACTION IN RESPONSE TO SAID COMPUTED SIGNALS ONLY WHEN THEY ARE OF AT LEAST SAID PREDETERMINED MINIMUM VALUE.