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Introduction to Thermal Conductivity Gas Analyzer

Gas industry terminology

It is an automatic continuous gas analyzer made by the principle that the total thermal conductivity of the mixed gas changes with the content of the measured component.

The thermal conductivity detector used is a bridge composed of two measuring cells to detect the change in the thermal conductivity of the gas at the outlet of the chromatographic column. The detector is sensitive to any kind of material that has a different thermal conductivity from the carrier gas, with a minimum detection limit of 0.5 × 1026 to 100 × 1026. The linear dynamic range is 103. It is suitable for the occasions where the thermal conductivity of the measured component is very different from that of other components.

A physical gas analysis instrument

Based on the principle that different gases have different heat conduction capabilities, it can estimate the content of certain components by measuring the thermal conductivity of the mixed gas. This kind of analytical instrument is simple and reliable, and it can be used for many kinds of gas. It is a basic analytical instrument. However, it is difficult to directly measure the thermal conductivity of a gas, so in practice, the change in the thermal conductivity of a gas is often converted into a change in resistance, and then measured by an electric bridge. There are two types of thermal sensors in thermal conductivity gas analyzers: semiconductor sensors and metal resistance wires. Semiconductor sensitive components have small volume, small thermal inertia, and large temperature coefficient of resistance, so they have high sensitivity and small time lag. On the platinum coil, a bead-shaped metal oxide is sintered as a sensitive element, and the same platinum coil with the same internal resistance and heat generation is wound as a compensation element (Figure 1). These two components form a bridge circuit as two arms, that is, a measurement circuit. When the semiconductor metal oxide sensitive element adsorbs the measured gas, the electrical conductivity and thermal conductivity change, and the heat dissipation state of the element changes accordingly. The change in element temperature changes the resistance of the platinum coil, and the bridge has an unbalanced voltage output, which can detect the gas concentration. Thermal conductivity gas analyzer has a wide range of applications. In addition to commonly used to analyze the content of hydrogen, ammonia, carbon dioxide, sulfur dioxide and low concentrations of flammable gases, it can also be used as a detector in a chromatograph to analyze other components.

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