| 摘要 |
1528721 Ionization smoke sensors CERBERUS AG 1 Feb 1977 [6 Feb 1976 (2) 14 Oct 1976] 03997/77 Heading G1N [Also in Divisions G4 and H 1] A fire sensor includes both a bipolar ionization gauge and a unipolar ionization gauge connected to an evaluation circuit which initiates an alarm condition when the resistance of at least one of the chambers exceeds a predetermined threshold. By using two chambers smouldering fires are detected and the effects of air speed are mitigated. The unipolar chamber U, see Division H1, comprises a grid housing, which gives unhindered access to air, provided with a radio-active source which has a range and so positioned and/or screened that bipolar ions are generated only within a limited area of the chamber the remainder only including ions of one polarity. The bipolar chamber B on the other hand comprises a radio-active source mounted in a housing substantially impermeable to air but through which air can enter only after being retarded and deflected whereby ions of both polarity are generated throughout the housing. Each chamber may be connected in series with a resistor across supply lines with the junctions therebetween connected to a threshold circuit Fig. 4 (not shown) or as shown in Fig. 6 to a reference chamber R, the junctions being connected to the gates of FET's T I , T 2 which are connected to an OR gate and switch S (thyristor) to generate an alarm signal. The three chambers may be continued into a mechanical unit Figs. 7, 8 (not shown). The sensor may be connected to control the frequency of an astable multi-vibrator Fig. 9. In the absence of smoke the frequency of the multi-vibrator is such that the charge on capacitor 16 is sufficient to keep transistor 18 ON whereby relay contacts 20 are kept open. If the resistance of either of the chambers increases due to smoke the frequency falls and the charge on capacitor 16 falls and transistor 18 switches OFF whereby relay 19 releases and contacts 20 close to operate an alarm. |
