| 摘要 |
1,204,708. Automatic alarm systems. GENERAL ELECTRIC CO. 12 Sept., 1967 [25 Nov., 1966], No. 41676/67. Heading G4N. [Also in Division G1] The presence of hydrogen or other reducing gas in air arising for example from incomplete combustion is detected by a detector comprising a substrate (1, Figs. 1, 2, not shown) one face of which is coated with a thin film metal oxide resistance element (5) on which is deposited an activating catalyst (6) in the form of small islands of thin film. On the other face is a thin film conductor element (4) for heating the substrate to within the range 200-380‹ C. Alternatively (Fig. 7, not shown) the substrate may be tubular. The resistance element (5) may be an oxide of tungsten, molybdenum, chromium, niobium, nickel, iron or titanium. The catalyst may be of platinum, iridium, rhodium, gold or palladium deposited by vacuum evaporation. The substrate may be quartz, alumina, beryllia, calcia silica glass or yttria. Indicator and alarm circuit.-The metal oxide reistance element 23, Fig. 5, forms with a selected one of capacitors C24, C25, C26, C27, and a neon lamp 28, a relaxation oscillator. In the presence of the catalyst hydrogen in the gas directed over the element 23 (e.g. by a pump) reacts with the metallic oxide of the element to change its resistance, and thus the time constant of the circuit changes. As ambient hydrogen concentration increases R23 decreases and 1/RC, which is proportional to the frequency of flashing of the tube, increases. At 10 c.p.s. to 20 c.p.s. the bulb appears to be lighted continuously. The instant this condition is reached corresponds to a definite value of R x C and since C and R are known an indication of the hydrogen concentration is obtained. An audio tone the frequency of which varies with hydrogen concentration may be used as an output indicator. In an alternative circuit, Fig. 4, the change in resistance of the metal oxide 16 controls an S.C.R. 15 to operate an alarm 14. |
