GB1123376A - A temperature sensing and a fire warning device - Google Patents

Abstract

1, 123,376. Measuring temperature electrically; photo-electric flame detectors. A.W. CROSSINGHAM. July 27, 1966 [Sept. 3, 1965] No. 37726/65. Headings G1A and G1N. A transistor 7, 8, and/or 9 is subjected to a temperature to be measured and its leakage current controls the collector current in an amplifying transistor 1, whose base is connected to the emitters of transistors 6, 7, 8 and which controls a meter 2, alarm relay 3, or a recorder. In a differential temperature measuring arrangement, a compensating temperature sensitive transistor or transistors (not shown) is or are arranged at a reference temperature and connected to the base circuit of the amplifying transistor 1 to supply a current in opposition to that from transistors 7, 8, 9. A plurality of the transistors 7, 8, 9 may be used as a temperature-responsive fire alarm system, and the base circuit of each transistor may include a photo-resistor 10,11,12 sensitive to the light of a flame, the effect of a drop on resistance of a photo-resistor due to a flame occurrence being such as to override the temperature responding operation. To avoid the photo-resistors causing operation of the relay 3 in response to permissible light such as daylight, a further photo-resistor 14 is connected in the voltage bias supply circuit and made responsive to the daylight but not flame-light, so that the base-bias voltage of the transistors 7, 8, 9 is automatically adjusted to null the effect of the daylight-induced drop in resistance of the photo-resistors 10, 11, 12. The bias voltage supply includes a Zener diode 15 and a potentiometer 13.