GB609874A - Improvements in apparatus for detecting changes in intensity of illumination - Google Patents

Abstract

609,874. Detecting smoke. FAULKNER, A. W. March 21, 1946, No. 8830. [Class 40 (iii)] Apparatus for effecting the operation of a relay in response to a decrease in the intensity of illumination falling on a photo-electric cell, such as occurs when smoke intervenes between the cell and a light source comprises a pair of photocells illuminated from a common source and one of the beams being subjected to the obscuring action and an instrument which on being operated by a differential current from the cells further obscures the light falling on one of them, this effect continuing until a relay circuit is closed. In the embodiment shown, two cells 15 and 18 are both illuminated by the same light source 10 and are connected in parallel opposition, a moving coil relay 20 being connected across them. The light falling on cell 15 passes both through a transparent channel carrying the air under test and through a hole 12 in the face of the moving coil relay. Should the channel become obscured, the resulting unbalance of the cells causes movement of the pointer 31 of the relay and a plate 22 mounted on this pointer moves to obscure partially the hole 12 further reducing the light falling on cell 15 causing still further movement of the pointer 31 until contacts 23 and 24 on the same spindle as the pointer 31 close and operate an alarm 26. The apparatus may be reset by opening switch 27 supplying the lamp 10. The Provisional Specification states that the smoke duct may be connected to a number of sources in turn by a motor-driven rotary member.