The catalytic combustion type sensor is a high temperature sensor, and the detection element of the catalytic element is formed by coating a platinum wire coil (φ0.025~φ0.05) with alumina and a binder to form a spherical shape, and is sintered, and the outer surface thereof is coated with platinum. Catalytic layer of rare metal such as palladium catalyzed combustion type combustible gas alarm sensor working principle Catalytic combustion type sensor is a high temperature sensor. The detection element of the catalytic element is coated with alumina on a platinum wire coil (φ0.025~φ0.05). And the binder is formed into a spherical shape and is sintered, and the outer surface thereof is coated with a catalytic layer of a rare metal such as platinum or palladium, and its structure is as shown in the figure.
The current is passed to the platinum wire to keep the detection element at a high temperature (300~400 °C). At this time, if it is in contact with the combustible gas such as methane gas, methane will be burned on the catalyst layer, and the combustion is essentially the adsorption of methane and adsorption on the surface of the element. The reaction between the oxygen ions, after the completion of the reaction, generates CO2 and H2O analysis, and the oxygen in the gas phase is adsorbed and dissociated by the element, replenishing the oxygen ions on the surface of the element.
The element is measured by the principle that the methane type is based on the measurement of the heat released by the methane combustion reaction on its surface, that is, the combustion causes the temperature of the platinum wire coil to rise, and the resistance value of the coil rises. The concentration of the flammable gas can be known by measuring the change in the resistance value of the platinum wire.
In practical applications, the Wheatstone bridge measurement circuit is often used, as shown in the figure. The black component in the bridge is both a detection component and the white component is a compensation component. The white component lacks only a catalyst layer compared to the black component, that is, the white component cannot be combusted when it encounters a combustible gas. Some manufacturers package black and white components in an explosion-proof network, and some manufacturers separately package them. When there is a certain concentration of combustible gas in the air, the resistance of the detecting element rises due to combustion, the bridge loses balance, and the voltage is output, which serves as a detecting function.
The combustibles burn under the action of a catalyst. Compared with direct combustion, the catalytic combustion temperature is lower and the combustion is more complete. The catalyst used for catalytic combustion is a noble metal and metal oxide multi-component material having a large specific surface. For example, a catalytic gas stove with a household load of Pd or a rare earth compound can reduce the CO content in the exhaust gas and improve the thermal efficiency. The 0.2% pt alumina catalyst is loaded, and most organic compounds can be burned at 500 ° C, and deodorized and purified to a chemical shift σ = 1 or less. Catalytic combustion is flameless combustion, so it is suitable for applications with high safety requirements, such as fuel cells using H2 and O2 as raw materials, and furnaces using gasoline or alcohol as raw materials (catalyst is immersed in Pt asbestos). For example, to eliminate NOx from chemical plants, fuel can be added to the smog, and catalytic combustion is used to convert NOx to N2 gas through supported platinum and palladium catalysts. A combustion method in which a combustible substance in a harmful gas is decomposed and oxidized at a lower temperature using a suitable catalyst.
The gas detector's sensor uses catalytic combustion to detect the gas, called a catalytic combustion sensor.
The detector for detecting combustible gas generally uses a catalytic combustion type sensor, which can be regarded as a miniaturized calorimeter whose detection principle has not changed greatly in a few decades. This is the structure of a Wheatstone bridge. A catalytic material is applied to its measuring bridge, which is not consumed during the entire measurement process. Even when the gas and vapor concentrations in the air are much lower than the LEL, they will undergo a catalytic combustion reaction on the bridge. When measuring, a voltage is applied to the reference and measurement bridges to heat up the catalytic reaction. The temperature is approximately 500 ° C or higher. Under normal conditions, the bridge is balanced, V1 = V2, and the output is zero. If a flammable gas is present, its oxidation process will cause the measuring bridge to be heated and the temperature to increase, while the reference bridge temperature will not change. The circuit will measure the change in resistance between them, V2 > V1, and the output voltage is proportional to the concentration of the gas to be measured.
Oxygen concentration is a must-have when measuring flammable and explosive gases. Catalytic sensors require at least 8-10% oxygen for accurate measurements. At 100% flammable gas concentration, the reading of this instrument will be 0% LEL! Therefore, in the measurement procedure, it is required to first measure the oxygen concentration before measuring the %LEL of the flammable and explosive gas. This is why it is necessary to measure both oxygen and LEL in confined space measurements. If the LEL value is measured completely without oxygen, it is easy to get erroneous results.
Catalytic combustion sensors can respond to most combustible gases. The heat generated by the combustion of a particular gas on a measuring bridge reflects its heat of combustion, which varies with the nature of the various materials. Therefore, different substances produce different instrument readings even at the same concentration. Keep in mind that the instrument measures changes in resistance rather than changes in concentration! The behavior of different gases on the measuring bridge can vary greatly. Usually, larger molecules produce more heat of combustion. On the other hand, smaller molecules are more likely to enter the sintered structure of the measuring head for reaction. Catalytic combustion sensors, especially those measuring %LEL, are not suitable for detecting "heavier" or long chain alkanes, especially those with high flash points. As mentioned earlier, it may be a good idea to use a photoionization detector at this time.
Shenzhen Suofong Industrial Co., Ltd. is a professional manufacturer of combustible gas alarms. For industrial explosion-proof combustible gas alarm devices, please contact Shenzhen Suofong Industrial Co., Ltd. support hotline.
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