GB884395A - Improvements in or relating to electronic condition-responsive apparatus - Google Patents

Abstract

884,395. Radiation detectors MINNEAPOLIS-HONEYWELL REGULATOR CO. Jan. 21, 1958 [Jan. 22, 1957], No. 2030/58. Class 40(3). Apparatus for detecting a condition manifested by the emission of light or like electromagnetic radiation, e.g. the presence of a flame at a burner, and operating indicator or control means in response to the detection, comprises a first transistor monostable circuit triggered by output pulses from a radiation sensitive device and an integrator, supplied with the output pulses of the monostable circuit, which produces a bias to hold a second transistor monostable circuit in its unstable condition in which it operates the indicator or control means. The presence of a flame at burner 10, Fig. 1, is detected by a photo-electric cell 11, which receives an alternating power supply from a secondary winding 20 of transformer 18, and each photo-cell output pulse increases the charge on condenser 24. When the voltage across the condenser reaches the firing voltage of gas tube 50, the tube fires discharging the condenser 24 and switching a monostable circuit comprising transistors 33 and 34 to its unstable state. This circuit switches back to its stable state after a time duration determined by condenser 48. The action is continuous and the output pulses of the monostable circuit, appearing across resistor 44, are integrated by resistor 16 and condenser 53 to provide a biasvoltage which maintains a second transistor monostable circuit comprising transistors 56 and 57 in its unstable state. A relay 59 in the collector circuit of transistor 57 is energised and operates indicator or control means. In a second arrangement, Fig. 2 (not shown), a Geiger counter, operating with a gas triode quenching circuit, detects the pressure of the flame.