Ultrasonic vehicle detector

Claim 1

IN A SYSTEM FOR DETECTING THE PRESENCE OF A VEHICLE AS IT MOVES ALONG A SELECTED PATH AND PASSES THROUGH A DETECTION ZONE THE COMBINATION COMPRISING, TRANSMITTING MEANS INCLUDING A TRANSDUCER FOR DIRECTING A ZONE-DEFINING BEAM OF ENERGY ACROSS A PATH WHICH IMPINGES UPON EACH VEHICLE AS IT MOVES THROUGH SAID ZONE BUT IMPINGES INSTEAD WHEN NO VEHICLE IS PRESENT UPON A FIXED REFLECTING SURFACE MORE DISTANT THAN SAID VEHICLE, RECEIVING MEANS INCLUDING TRANSDUCER MEANS BEING POSITIONED AND DIRECTED TO RECEIVE REFLECTIONS OF SAID BEAM ALTERNATIVELY FROM EACH VEHICLE AND FROM SAID FIXED SURFACE, SAID RECEIVING MEANS PRODUCING AN OUTPUT HAVING AT LEAST ONE DISTINCTIVE CHARACTERISTIC THEREOF VARYING IN ACCORDANCE WITH THE AMPLITUDE OF THE REFLECTED ENERGY RECEIVED BY SAID RECEIVING MEANS AND DETECTION MEANS BEING GOVERNED ACCORDING TO SAID DISTINCTIVE CHARACTERISTIC OF SAID OUTPUT OF SAID RECEIVING MEANS AND BEING CONTROLLED TO A DISTINCTIVE CONDITION INDICATIVE OF THE PRESENCE OF A VEHICLE IN SAID ZONE ONLY WHEN SAID DISTINCTIVE CHARACTERISTIC HAS THE VALUE IT ASSUMES WHEN SAID AMPLITUDE OF SAID REFLECTED ENERGY IS IN EXCESS OF THAT NORMALLY RECEIVED FROM SAID FIXED REFLECTING SURFACE WHEN NO VEHICLE IS PRESENT.