Optical pyrometers

Claim 1

AN OPTICAL PYROMETER SYSTEM FOR CONTROLLING THE TEMPERATURE OF A FURNACE CONTAINING A HEAT SOURCE, COMPRISING A SCREEN HAVING AN OPENING THEREIN, AN OPTICAL SYSTEM FOR PROJECTING AN IMAGE OF SAID HEAT SOURCE ON THE FACE OF SAID SCREEN, SAID IMAGE BEING LARGER THAN SAID OPENING, A FILAMENT, MEANS FOR HEATING SAID FILAMENT TO OBTAIN A STANDARD BRILLIANCE, SAID OPTICAL SYSTEM BEING FURTHER ADAPTED TO PROJECT AN IMAGE OF SAID FILAMENT ON THE FACE OF SAID SCREEN, SAID OPENING EXCEEDING THE CORRESPONDING DIMENSION OF SAID FILAMENT IMAGE IN ONE DIRECTION, THE LATTER IMAGE BEING SUPERPOSED UPON A PORTION OF SAID HEAT SOURCE IMAGE TO FORM A COMPOSITE IMAGE, A VIBRATOR ENERGIZED FROM AN A.C. REFERENCE SOURCE FOR OSCILLATING SAID SCREEN IN SAID DIRECTION, PHOTOELECTRIC MEANS ADAPTED TO PRODUCE A CURRENT PROPORTIONAL TO THE LIGHT INCIDENT THEREON, SAID OPENING ADMITTING LIGHT TO SAID PHOTOELECTRIC MEANS FROM THE SUPERPOSED PORTION OF SAID COMPOSITE IMAGE AT ONE EXTREME OF SCREEN OSCILLATION AND FROM THE NON-SUPERPOSED PORTION AT THE OTHER EXTREME, MEANS FOR COMPARING THE PHASE OF THE PHOTOELECTRIC CURRENT AGAINST THAT OF SAID A.C. REFERENCE SOURCE TO OBTAIN AN OUTPUT SIGNAL, A MOTOR RESPONSIVE TO THE PHASE OF SAID OUTPUT SIGNAL, A CURRENT SOURCE ADAPTED TO SUPPLY SAID HEAT SOURCE, AND MEANS MECHANICALLY COUPLED TO SAID MOTOR FOR REGULATING THE AMOUNT OF HEATING CURRENT APPLIED TO SAID HEAT SOURCE.