| 摘要 |
1308873 Ionization smoke detectors NITTAN CO Ltd 10 Sept 1971 [14 Sept 1970] 42290/71 Heading G1N [Also in Division H1] In the ionization smoke detector shown in Fig. 1 the FET 5 used consists of an electroded semiconductor body encapsulated in a moulded body of silicone resin from opposite faces of which the gate, and the drain end source conductors respectively emerge at points 10 mm. apart along the resin surface. Such an FET can be used exposed to the ambient without danger of the gate-source resistance falling sufficiently to cause false operation of the alarm. The alarm device is connected in series with a constant voltage source across terminals 1 and 2, 10 and 20 representing closed and open ionization chambers respectively comprising radio-active sources 13, 23. Entry of smoke into chamber 20 raises its resistance causing the FET to conduct sufficiently to trigger an SCR 8 via zener diode F and hence operate the alarm. |
