The structure of contact combustion gas sensor and the circuit of household flammable gas alarm

High-purity platinum wire is wound into a coil. In order to make the coil have an appropriate resistance (1Ω～2Ω), it should generally be wound more than 10 times. A paste coating composed of aluminum oxide or aluminum oxide and silicon oxide is applied to the outside of the coil, and after drying, it is sintered at a certain temperature to form a spherical porous body. The sintered small balls are placed in a salt solution of precious metals such as platinum and palladium, and are fully immersed and then taken out and dried. Then, after high-temperature heat treatment, a precious metal catalyst layer is formed on the aluminum oxide (aluminum oxide silicon oxide) carrier, and finally assembled into a gas sensor. In addition, the precious metal catalyst powder can also be fully mixed with aluminum oxide, silicon oxide and other carriers to form a paste, which is applied to the coil wound by platinum wire and directly fired for use. In addition, the size and resistance of the platinum coil as a compensation element should be the same as those of the detection element. In addition, an aluminum oxide or silicon oxide carrier layer should also be coated, but there is no need to immerse in a precious metal salt solution or mix in a precious metal catalyst powder to form a catalyst layer.

(a) Internal schematic diagram of the element (b) External diagram of the sensitive element
Schematic diagram of the structure of the contact combustion type gas sensitive element

Household flammable gas alarm circuit

The figure above is an application circuit with a series buzzer. As the concentration of combustible gas in the environment increases, the resistance of the gas sensor drops to a certain value, and the current flowing into the buzzer is sufficient to drive it to work and send out an alarm signal.