Hall Effect tester for heated window grids

A solid state electrical continuity test probe instrument for detecting breaks in a plurality of electrically connected conductive resistive defroster grid lines located on a window glass plate installed in a motor vehicle, said grid lines elongated in a common first direction and uniformly transversely spaced from each other a predetermined first distance on the inside surface of the window glass plate area to be heated, a DC voltage source of the vehicle connected to said grid lines providing substantially equal currents passing through each grid line for heating the plate area, said instrument comprising:

• a probe housing suitable for hand-held operation including a sensing frontal end having a substantially planar glide surface;
• said housing including first and second Hall Effect sensors arranged on an axis parallel to said glide surface;
• said sensors spaced on said axis with their centers located a predetermined second distance less than said predetermined first distance between the transversely spaced grid lines;
• said instrument characterized in that with said glide surface positioned in flush intimate contact with the outside surface of the vehicle window glass plate area and with said axis of the sensors oriented substantially transverse to the grid lines, said probe sensors adapted to be moved along the plate area in a direction transverse to said common first direction successively crossing each grid line;
• whereby said first sensor is caused to alternately enter and depart maximum and minimum conducting grid line flux density regions while said second sensor is caused to concurrently enter and depart minimum and maximum conducting grid line flux density regions and so forth;
• solid state detection circuit means within said housing supplied for a secondary DC power source, said circuit means operative for receiving and amplifying the phase difference in sinusoidal output voltage signals from said sensors to provide a composite sinusoidal output signal, and said circuit means including comparator means producing an output triggering pulse operative for successively activating and deactivating indicating means on said probe housing informing the operator of the state of electrical continuity of each successive grid line being traversed by said sensors, thereby obviating the need for the operator to enter the vehicle to conduct a continuity test of said grid lines with said probe instrument.