| 摘要 |
A catalytic gas detector for detecting flammable gases comprises a Wheatstone bridge circuit formed on a silicon substrate 10. The silicon substrate is coated with an insulating layer 12 of silicon nitride. The Wheatstone bridge is formed as an electrically conductive track deposited on the layer of silicon nitride. It consists of resistive heating sensing element 24 and compensating element 26 and resistors 34 and 36 connected together by leads 28. The sensing element 24 is formed as a meanandering track of platinum coated with a ceramic substrate 30 bearing catalyst material. The compensating element 26 is similar to the sensing element 24 except that the substrate 32 is inert. An electric current is passed through the bridge circuit to cause the resistive heating elements 24 and 26 to be heated to the operating temperature. When a flammable gas is present, it oxidises exothermically on the catalyst bearing substrate 30 causing the temperature of the sensing element 24 to rise compared with the termperature of the compensating element 26. The temperature difference gives rise to a difference in electrical resistance of the elements 24 and 26 which is detected by the Wheatstone bridge to indicate the presence of the flammable gas. The sensing element 24 and the compensating element 26 are formed on bridge portions 20 and 22 of the nitride layer 12 where some or all of the underlying silicon 10 has been removed. A slot 18 is formed between the bridge portion 20 and 22 to reduce heat loss from the sensing element 24.
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