Temp. rise detector for fire alarm - has differential amplifier triggering thyristor in lamp circuit when temp. unbalance in two semiconductor diodes occurs

摘要

Semi conductor junctions exhibit constant decrease in voltage as temperature increases. This effect is utilised in the fire detector where constant performance is required over large ambient temperature range. A diode (1) is coupled to thermal ambient environment under surveillance while a second diode (2) is isolated. The diode anodes are connected to a differential input amplifier (6) and a potentiometer (5) with a resistor (3, 4) network providing diode polarisation current to enable negative output to be set at amplifier output. Temperature unbalance in diodes causes positive output voltage from the amplifier t trigger a thyristor (8) to cause a lamp (9) to illuminate.