Magnetically triggered elapsed time indicator

Apparatus for issuing a timing signal when a water vehicle travels past a magnetic field centered at a fixed point, the vehicle defining a longitudinal dimension in the direction of travel, said apparatus comprising:

• first and second coils carried by the vehicle and spaced apart a known distance longitudinally, said coils producing first and second output signals, respectively, substantially similar in form, in response to movement of the coils in the magnetic field past the point;
• means for comparing said first and second output signals and for producing a pulse only when said first and second output signals are displaced in time;
• and,
• means for issuing said timing signal in response to said pulse.

Apparatus for determining elapsed time for a moving water vehicle to travel past magnetic markers, said apparatus comprising:

• first and second transducers spaced apart on the vehicle for producing first and second electrical outputs, respectively, in response to movement of said transducers in a magnetic field;
• a discriminator coupled to said transducers for rejecting simultaneous spurious outputs inconsistent with movement of said vehicle past one of the markers;
• and,
• means for determining the elapsed time based only on outputs not rejected.

Apparatus for determining elapsed time for a moving water vehicle to travel between fixed points characterized by magnetic fields, said apparatus comprising:

• at least one magnetic-field peak detector including first and second sensors carried by the vehicle and spaced apart a known distance in the direction of travel, said at least one peak detector producing first and second peak detection outputs, respectively, in response to movement of the first and second sensors in a magnetic field;
• means for rejecting simultaneous outputs inconsistent with movement of the vehicle in the direction of travel, and for recording the occurrence of acceptable outputs not rejected;
• and,
• means for determining the elapsed time based on said recorded occurrences of acceptable outputs.

Apparatus for determining elapsed time for a moving water craft to travel between magnetic markers, said apparatus comprising:

• first and second coils carried by the water craft and spaced apart a known distance in the direction of travel between the markers, said coils producing first and second outputs, respectively, in response to movement of the coils in a magnetic field;
• means for rejecting substantially simultaneous outputs of said coils caused by movement of said water craft in the earth's magnetic field:
• and,
• means for determining the elapsed time based only on outputs not rejected.

Apparatus for determining a valid elapsed time for a moving water vehicle to travel between two fixed points characterized by separate magnetic fields, said apparatus comprising:

• at least one magnetic-field peak detector including first and second sensors carried by the vehicle and spaced apart a known distance in a direction of travel, said at least one peak detector producing a first set of first and second peak detection outputs, respectively, in response to movement of the first and second sensors in the magnetic field past one of the fixed points, and a second set of first and second peak detection outputs, respectively, in response to movement of the first and second sensors in the magnetic field past the other of the fixed points;
• means for rejecting sets of first and second outputs inconsistent with movement of the vehicle in the direction of travel, and for identifying sets of acceptable outputs not rejected;
• and,
• means for initiating measurement of elapsed time when a first set of acceptable outputs is identified, and for terminating the measurement of elapsed time when a second set of acceptable outputs is identified;
• and,
• means using a predetermined lower limit of the elapsed time for ignoring any outputs during measurement of the elapsed time before the lower limit.