Method and apparatus for vehicle detection

Claim 1

IN A SYSTEM FOR ANALYZING THE FLOW OF VEHICULAR TRAFFIC ALONG A PATH CIRCUMSCRIBING AT LEAST A PORTION OF THE EARTH''S SURFASCE THE COMBINATION OF: MAGNETIC FIELD SENSING MEANS POSITIONED AT A PREDETERMINED DISTANCE FROM SAID PATH AT WHICH THE EFFECT OF THE PASSAGE OF A VEHICLE ALONG SAID PATH PRODUCES VARIATIONS IN THE EARTH''S MAGNETIC FILED INTENSITY, ONLY THE FIRST AND LAST INTENSITY VARIATIONS FALLING BELOW THE AMBIENT INTENSITY OF SAID FIELD OBTAINING IN THE ABSENCE OF A VEHICLE; A THRESHOLD CIRCUIT COUPLED TO SAID MAGNETIC FIELD SENSING MEANS; AND A CIRCUIT COUPLED TO SAID THRESHOLD CIRCUIT WHICH IS ACTUATED IN RESPONSE TO INDIVIDUAL VEHICLES PASSING ALONG SAID PATH; SAID THRESHOLD CIRCUIT INCLUDING MEANS ESTABLISHING A FIRST PREDETERMINED THRESHOLD LEVEL OF OPERATION; AND MEANS RESPONSIVE TO THE APPEARANCE OF A SIGNAL IN EXCESS OF SAID FIRST PREDETERMINED THRESHOLD LEVEL FOR LOWERING SAID THRESHOLD LEVEL OF OPERATION TO A SECOND PREDETERMINED LEVEL LESS THAN SAID FIRST PREDETERMINED LEVEL.

Claim 2

A METHOD OF USING A DETECTOR PROVIDING A SIGNAL WHOSE AMPLITUDE IS SUBSTANTIALLY PROPORTIONAL TO MAGNETIC FIELD INTENSITY FOR INDICATING THE PRESENCE OF A VEHICLE, COMPRISED OF SPACED FIRST AND SECOND MASSES OF MAGNETICALLY PERMEABLE MATERIAL, AT ANY POSITION OF SAID VEHICLE BETWEEN FIRST AND SECOND POSITIONS ON A PATH WHICH PATH CIRCUMSCRIBES AT LEAST PORTION OF THE EARTH''S SURFACE, SAID METHOD COMPRISING THE STEPS OF: POSITIONING SAID DETECTOR AT A POSITION RELATIVE TO SAID PATH WHEREAT THE PRESENCE OF A VHEICLE AT ANY POSITION OF SAID VEHICLE IN CLOSE PROXIMITY TO SAID DETECTOR POSTION INCREASES THE MAGNETIC FIELD INTENSITY AT SAID DETECTOR POSITION FROM AN AMBIENT FIELD INTENSITY LEVEL EXISTING THEREAT IN THE ABSENCE OF SAID VEHICLE; AND INDICATING THE PRESENCE OF A VEHICLED IN RESPONSE TO THE AMPLITUDE OF SAID SIGNAL EXCEEDING THE AMPLITUDE OF SAID SIGNAL IN THE ABSENCE OF SAID VEHICLE.