GB1069023A - Fire detecting device - Google Patents

Abstract

1,069,023. S.T. selective signalling; lamp failure alarms. AMERICAN DISTRICT TELEGRAPH CO. July 7, 1965 [Aug. 27, 1964], No. 28865/65. Headings G4H and G4N. [Also in Division G1] A fire detecting device includes a smoke detector comprising a chamber through which smoke can flow causing light to be scattered on to a photo-cell which is shielded from direct exposure by the light source, the latter being arranged to produce a beam of substantially rectangular elongated cross-section. The device can be used in factories &c., in conjunction with a code transmitter to send information from the device by a telephone link to a central alarm station or can be modified for domestic use. Constructional details.-The smoke detector chamber is mounted within a well-perforated protective cover which most suitably is ceiling- mounted. The chamber comprises a box with open sides, which are provided with two pairs of cover units (28, 33) (Fig. 1, not shown) arranged to form with the top, bottom and ends of the box, two pairs of entry and exit ports for smoke. The box is spaced from the ceiling to prevent back pressure of escaping smoke reducing the through-flow. The light source, a filament lamp operated at low voltage to emit mainly infra-red is carried in a shroud outside one end of the box and light is directed by lens (44) into a light trap at the other end where excessive reflections of the beam in the chamber are suppressed. The lamp, whose filament is U-shaped, is orientated such that the beam is elongated and rectangular in cross-section. One or more photo-cells (37) may be mounted in the chamber, each occupying one end of a tube (36) which enters the chamber through a side cover. Thus, normally, light is prevented from reading the photo-cell from the beam which is at right-angles to the tube axis. The presence of smoke in the chamber allows scattered light to enter the tube and reach the detector. Operation in conjunction with central alarm station (Fig. 4, not shown).-The circuit associated with the device includes an alarm circuit and a code transmitter. Exposure, to scattered light, of the photo-cell(s) (37), results in a decrease in its resistance and the corresponding current increase is amplified by transistors (T 1 , T 2 ) to energize a relay (AL). This causes energization of an alarm lamp (49) and of an audible alarm and also closes a switch in the transmitter circuit, resulting in energization of relay (9) and transmission of a coded alarm to the central station. A thermostat (T) is provided in the circuit to operate the same alarms if an abnormal heat rise occurs, unaccompanied by smoke. An alarm representing failure of the lamp (39) can be transmitted to the central station by having a relay winding (TR) operating on the transmitter in series with the lamp. Testing of the system is carried out by closing a magnetically operated switch (S) (mounted near the chamber) or a remote pushbutton switch (69), causing brightening of the lamp to generate light scattering from the chamber walls sufficient to operate the alarms. Operation in domestic application (Figs. 5, 6. not shown).-The alarm circuit is supplied by rectified A.C. The alarm actuated is a horn and a thermostat is provided as before. An added feature, which could be applied in the commercial design, is a photo-cell provided with a red filter, and mounted on the protective cover (15), to act as a flame detector. The test system for the device utilizes an extra light source (74) mounted within the chamber and connected in series with a light-sensitive transistor switch (73) mounted opposite the main light source (39). On closing a switch to light lamp (74), the alarm should sound. If the main lamp (39) has failed &c., the switch (73) is not switched on or the alarm fails to sound.