Thickness gage for blast furnace wall

Claim 1

IN A FURNACE HAVING AT LEAST ONE WALL OF GIVEN ELECTRICAL CONDUCTIVITY, WHICH WALL IS REDUCED IN THICKNESS OVER A PERIOD OF TIME BY THE ABRASION OF CHARGES DELIVERED TO THE FURNACE AND MEASURING MEANS ARE UTILIZED TO SENSE SUCH THICKNESS REDUCTION, SAID FURNACE WALL HAVING A CERTAIN PREDETERMINED THICKNESS, A PAIR OF ELECTRICAL CONDUCTORS CARRIED IN SAID FURNACE WALL AND POSITIONED GENERALLY PERPENDICULAR TO THE WALL, SAID CONDUCTORS BEING POSITIONED IN A SPACED-APART RELATIONSHIP TO EACH OTHER AND ONE END OF EACH OF SAID CONDUCTORS EXTENDING THROUGH SAID WALL TO THE EXTERIOR THEREOF, A PLURALITY OF RESISTANCE ELEMENTS OF PREDETERMINED RESISTANCE, SAID RESISTANCE ELEMENTS CONNECTED BETWEEN SAID CONDUCTORS IN AN ELECTRICALLY PARALLEL RELATIONSHIP, EACH OF SAID RESISTANCE ELEMENTS EXHIBITING AN ELECTRICAL CONDUCTIVITY HIGH WITH RESPECT TO SAID GIVEN CONDUCTIVITY OF THE WALL, EACH BEING POSITIONED IN A PREDETERMINED SPACED-APART RELATIONSHIP TO EACH OTHER, AND EACH RESISTANCE ELEMENT BEING DISPOSED GENERALLY PARALLEL TO THE FURNACE WALL, WHEREBY SAID CONDUCTORS AND SAID ELEMENTS WILL BE ABRADED AWAY WITH SAID WALL, AND MEANS, INCLUDING THE CONDUCTOR ENDS EXTENDING TO THE EXTERIOR OF SAID WALL, FOR COUPLING SAID MEASURING MEANS TO SAID CONDUCTORS FOR MEASURING THE THICKNESS OF SAID WALL BY MEASURING THE TOTAL RESISTANCE OF SAID PARALLEL-CONNECTED RESISTANCE ELEMENTS AS SAID WALL IS REDUCED IN THICKNESS BY ABRASION.