Temperature sensing device

Claim 1

A PYROMETRIC DEVICE FOR USE WITH A CLOSED FURNACE HAVING INSULATED WALLS, COMPRISING A SOURCE OF ELECTRICAL ENERGY LOCATED OUTSIDE SAID FURNACE, INDICATOR MEANS LOCATED OUTSIDE SAID FURNACE, A HEAT RESISTANT ELECTRICALLY NONCONDUCTIVE MEMBER INCLUDING A U-SHAPED PASSAGE THEREIN ARRANGED SUCH THAT THE ONE EXTREMITIES OF THE LEGS THEREOF TERMINATE AT AN EDGE OF SAID MEMBER, A PAIR OF CURRENT CONDUCTING ELEMENTS, EACH OF SAID CONDUCTING ELEMENTS EXTENDING INTO ONE OF THE LEGS OF SAID U-SHAPED PASSAGE WITH THEIR FREE ENDS TERMINATING AT THE PORTION OF SAID U-SHAPED PASSAGE THAT JOINS SAID LEGS, A SOLID MIXTURE DISPOSED WITHIN SAID PASSAGE IN CONTACT WITH THE INNER TERMINAL ENDS OF SAID CURRENT CONDUCTING ELEMENTS, SAID SOLID MIXTURE BEING SUBSTANTIALLY NONCONDUCTIVE IN THE SOLID STATE AND BECOMING CONDUCTIVE UPON CHANGE TO THE LIQUID PHASE AT A PREDETERMINED TEMPERATURE BY ABSORPTION OF HEAT FROM WITHIN SAID FURNACE, AND MEANS PASSING THROUGH THE INSULATED WALLS OF SAID FURNACE AND CONNECTING SAID SOURCE OF ELECTRICAL ENERGY AND SAID INDICATOR MEANS TO SAID CURRENT CONDUCTING ELEMENTS, THE CIRCUIT FORMED BEING NORMALLY OPEN AND CLOSING WHEN THE TEMPERATURE INSIDE THE FURNACE REACHES SAID PREDETERMINED TEMPERATURE, WHEREBY THE CURRENT PASSING THROUGH SAID MIXTURE AND BETWEEN THE INNER TERMINAL ENDS OF SAID CURRENT CONDUCTING ELEMENTS ACTIVATES SAID INDICATOR MEANS.