VAPOR OR PARTICLE DETECTION DEVICE
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Abstract
A VAPOR, SMOKE OR PARTICLE DETECTION DEVICE OF THE TYPE COMPRISING A BLACK-WALLED CHAMBER CONTAINING A LIGHT SOURCE AND A PHOTOCONDUCTIVE CELL, ARRANGED TO DETECT LIGHT FROM THE SOURCE WHEN REFLECTED FROM PARTICLES PRESENT IN THE CHAMBER, AND INCLUDING A SELF-BALANCING CONTROL CIRCUIT FOR ACTUATING AN ALARM WHEN THE DETECTION SIGNAL FROM THE PHOTOCONDUCTIVE CELL EXCEEDS A GIVE LEVEL. THE SENSITIVITY OR THRESHOLD LEVEL OF THE ALARM CONTROL CIRCUIT IS MAINTAINED CONSTANT DESPITE WIDE VARIATIONS IN THE APPLIED OPERATING VOLTAGE BY MEANS OF A VOLTAGE DIVIDING BRIDGE AR-
RRANGEMENT USING AN INSULATED-GATE FIELD EFFECT TRANSISTOR FOR OPERATING THE GATE OF A CONTROLLED RECTIFIER WHICH CONTROLS CURRENT FLOW TO THE ALARM DEVICE. ALSO PROVIDED IN COMBINATION ARE MEANS FOR INTERMITTENTLY OPERATING THE LIGHT SOURCE FOR LONGER BATTERY LIFE, A HIGH TEMPERATURE DETECTION ELEMENT AND A FAIL-SAFE MECHANISM FOR SIGNALLING WHEN THE DEVICE IS INOPERATIVE.
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