Patent GB-987995-A (GB)
Title: Improvements in or relating to ionization fire alarm system
IPC: G01N27/66
Filed: 1961-11-01
Abstract: 987,995. Detecting smoke presence. SECURITON A.G. Nov. 1, 1961 [Nov. 2,1960; Oct. 6, 1961], No. 39173/61. Heading G1N. [Also in Division G4] An ionization fire alarm system has a plurality of fire detecting units M1-Mn each of which includes a closed ionization chamber (as at K 2 <SP>1</SP>) series connected with an open ionization chamber (as at K 1 <SP>1</SP>), the air ionization thereof being variable in response to combustion gases to actuate an alarm signal by means of a triode tube R÷<SP>1</SP>. The system comprises a temperature responsive device TG1 associated with each fire detecting unit and operating in response to a predetermined limit temperature independently of the presence of combustion gases, a grid electrode SG1 arranged in the open ionization chamber for checking the readiness of operation of the fire detecting unit and a calibrated indicator A for indicating the operating conditions of the fire alarm system, the lighting up of the triode tube of a fire detector unit being visible from the exterior so as to indicate the operating condition of each fire detecting unit. The device TG1 responding independently to temperature may consist of a spring loaded fusible element. When the element fuses contacts tg<SP>1</SP> are closed and the grid of the tube R÷<SP>1</SP> is connected to the positive supply U1 through resistor R 2 <SP>1</SP>, causing the tube to ignite. For testing the apparatus the key PT is connected to a positive supply U2 so that the grid Sg1 becomes positively charged. This increases the ionization in the open chamber K 1 <SP>1</SP> and causes the tube R o 1 to strike if the system is functioning properly. The indicator A at the central station indicates the different operating states including readiness and alarm, of the system. The detector unit is contained in a housing 6 (Fig. 2) which fits by means of terminal pins 7-10 into tube sockets 2 and 3. The housing 6 forms the cathode of an open ionization chamber F3, with an anode 14 disposed centrally and an intermediate grid 15, to which is also attached a ring 16. The ring carries radiation sources 17, 18, which produce ionisation in the open chamber 13, and may be partially shielded by shutter rings 19, 10. A fusible element 21 is included in the anode 14, which is spring loaded at the end 22. If the melting temperature of the element 21 is reached, the anode 14 is brought into contact with the plate 23 connected to the positive supply. The closed ionisation chamber at 24 has a sleeve like cathode 25 with a radiation source disposed on its inner surface, and an anode 27 arranged as a helix placed centrally. This chamber is fixed on one side of a high insulating tube case 28, which has a triode tube 29 mounted on its other side. Appropriate potentials are provided via the pins 7-10. Slots are provided in the housing 6 (Figs. 4 and 5 not shown) to permit the entry of combustion gases to the chamber 13. Should this happen the ionisatin present in the chamber 13 is so changed that the voltage of the anode 14 is increased so as to ignite the tube and trigger the alarm.