Method of and apparatus for controlling heating element temperature

Claim 1

APPARATUS FOR MAINTAINING FIRST AND SECOND A.C. ELECTRICAL HEATING ELEMENTS ENERGIZED FROM THE SECONDARY COIL OF POWER TRANSFORMER HAVING A PRIMARY AND A SECONDARY COIL AT PREDETERMINED TEMPERATURES, SAID APPARATUS COMPRISING: FIRST CIRCUIT MEANS INCLUDING A FIRST TEMPERATURE CONTROLLER, A FIRST TEMPERATURE RESPONSIVE ELEMENT, AND A SATURABLE MEANS, ARRANGED TO REGULATE SAID POWER TRANSFORMER IN RESPONSE TO TEMPERATURE SIGNALS FROM SAID FIRST A.C. ELECTRICAL HEATING ELEMENT; SAID POWER TRANSFORMER SECONDARY COIL BEING ELECTRICALLY CONNECTED AT ONE END TO ONE SIDE OF SAID FIRST A.C. ELECTRICAL HEATING ELEMENT AND AT THE OTHER END TO ONE SIDE OF SAID SECOND A.C. ELECTRICAL HEATING ELEMENT; SAID POWER TRANSFORMER SECONDARY COIL HAVING A PLURALITY OF VOLTAGE TAPS; A CONTROL TRANSFORMER HAVING A PRIMARY COIL AND A SECONDARY COIL; CIRCUIT MEANS FOR ALTERNATELY CONNECTING ONE OF SAID VOLTAGE TAPS TO ONE END OF SAID CONTROL TRANSFORMER PRIMARY COIL; CIRCUIT MEANS TO CONNECT ONE SIDE OF SAID FIRST A.C. ELECTRICAL HEATING ELEMENT, ONE SIDE OF SAID SECOND A.C. ELECTRICAL HEATING ELEMENT, AND ONE END OF SAID CONTROL TRANSFORMER PRIMARY COIL TO A COMMON GROUND; SAID CONTROL TRANSFORMER SECONDARY COIL BEING ELECTRICALLY CONNECTED TO A SECOND TEMPERATURE CONTROLLER CONSTRUCTED AND ARRANGED TO VARY THE IMPEDANCE ON SAID CONTROL TRANSFORMER SECONDARY COIL IN RESPONSE TO TEMPERATURE SIGNALS; A SECOND TEMPERATURE RESPONSIVE ELEMENT CONNECTED TO SAID SECOND A.C. ELECTRICAL HEATING ELEMENT AND CONNECTED TO SAID SECOND TEMPERATURE CONTROLLER TO TRANSMIT TEMPERATURE SIGNALS FROM SAID SECOND A.C. ELECTRICAL HEATING ELEMENT TO SAID SECOND TEMPERATURE CONTROLLER; SAID FIRST AND SECOND TEMPERATURE CONTROLLERS EACH BEING SET TO MAINTAIN SAID FIRST AND SECOND A.C. ELECTRICAL HEATING ELEMENTS AT PREDETERMINED TEMPERATURES.