Temperature sensitive bridge circuits

Claim 1

CONTROL APPARATUS COMPRISING A BRIDGE CIRCUIT INCLUDING A POWER TRANSFORMER HAVING A TAPPED SECONDARY WINDING, A SERIES CIRCUIT INCLUDING A RESISTANCE ELEMENT MEANS CONNECTED IN SERIES WITH AN IMPEDANCE ELEMENT HAVING A NEGATIVE TEMPERATURE COEFFICIENT, MEANS CONNECTING THE ENDS OF SAID SERIES CIRCUIT TO SAID SECONDARY WINDING, SAID BRIDGE CIRCUIT HAVING OUTPUT TERMINALS PROVIDED BY SAID TAP AND BY THE POINT OF CONNECTION OF SAID RESISTANCE ELEMENT AND SAID IMPEDANCE ELEMENT AND PROVIDING AN OUTPUT SIGNAL AT SAID TERMINALS WHICH IS POSITIVE OR NEGATIVE DEPENDENT ON WHETHER THE RATIO OF THE VALUE OF SAID IMPEDANCE ELEMENT TO THE VALUE OF SAID RESISTANCE ELEMENT IS LESS OR GREATER THAN UNITY; AN ELECTRON DISCHARGE DEVICE HAVING AN ANODE, CATHODE AND CONTROL ELEMENT; MEANS CONNECTING SAID CONTROL ELEMENT TO ONE OF SAID OUTPUT TERMINALS AND MEANS CONNECTING SAID CATHODE TO THE OTHER OF SAID OUTPUT TERMINALS; AND MEANS CONNECTING SAID ANODE TO SAID SECONDARY WINDING AT SAID END THEREOF CONNECTED TO SAID IMPEDANCE ELEMENT TO RENDER SAID ELECTRON DISCHARGE DEVICE CONDUCTING IN RESPONSE TO ONE PHASE OF THE OUTPUT SIGNAL OF SAID BRIDGE CIRCUIT CORRESPONDING TO TEMPERATURES ABOVE ONE LIMIT AND NONCONDUCTING AT TEMPERATURES LESS THAN SAID LIMIT.