Application of Sensor in Gas Detector for Thermal Conductivity
First, the application of the sensor in the detector
A sensor is usually defined as "a device that converts a sensed physical quantity (generally non-electricity) into another physical quantity (generally electric quantity) and outputs it according to the corresponding relationship for the purpose of measurement." The sensor is the first link and the vanguard to realize the test and control. Without the sensor to accurately and reliably capture and convert the original information, it is impossible to talk about any accurate test and control. The position of the sensor in the detection system is shown in the figure.
2. Industry definition
The thermal conductivity gas detector is an instrumentation tool for gas concentration detection. It is an automatic continuous gas analyzer made of the principle that the total thermal conductivity of the mixed gas changes with the content of the measured components. Gas detection instruments convert the physical or chemical non-electrical signals collected by the gas sensor into electrical signals, and then rectify and filter the above electrical signals through external circuits, and control the corresponding modules through these processed signals to realize gas detection. various specific functions. The gas detector can detect and analyze hydrogen, hydrogen sulfide, carbon monoxide, oxygen, sulfur dioxide, phosphine, ammonia, nitrogen dioxide, hydrogen cyanide, chlorine, chlorine dioxide, ozone and combustible gases and other gases.
3. Working principle
Thermal conductivity gas detector is a kind of physical gas detection instrument. According to the principle that different gases have different thermal conductivity, it calculates the content of some components by measuring the thermal conductivity of the mixed gas. This detection instrument is simple and reliable, applicable to many types of gases, and is a basic detection instrument. However, it is difficult to directly measure the thermal conductivity of gas, so in fact, the change of thermal conductivity of gas is often converted into the change of resistance, and then measured with a bridge. The heat sensitive elements of the thermal conductivity gas detector mainly include semiconductor sensitive elements and metal resistance wires. The semiconductor sensitive element has small volume, small thermal inertia, and large temperature coefficient of resistance, so it has high sensitivity and small time lag.
The bead-shaped metal oxide is sintered on the platinum coil as the sensitive element, and then the same platinum coil with equal internal resistance and calorific value is wound with a non-reactive material to the gas as the compensation element. These two components form a bridge circuit as two arms, which is the measurement circuit. When the semiconductor metal oxide sensitive element absorbs the measured gas, the electrical conductivity and thermal conductivity will change, and the heat dissipation state of the element will also change accordingly. The temperature change of the element changes the resistance of the platinum coil, and the bridge then has an unbalanced voltage output, which can detect the concentration of the gas. Thermal conductivity gas detectors have a wide range of applications. In addition to being commonly used to detect hydrogen, ammonia, carbon dioxide, sulfur dioxide and low-concentration flammable gases, they can also be used as detectors in chromatographic analyzers to analyze other components.
4. Application field
According to the differences in the application fields of thermal conductivity gas detection instruments, gas detection instruments are mainly divided into two series: industrial gas detection instruments and civilian gas detection instruments. Industrial gas detection instruments are divided into three categories: portable, fixed and system. Industrial gas detection instruments and meters are mainly used in petroleum, chemical, metallurgy, coal mines, liquefied gas and other enterprises; civilian gas detection instruments are mainly used in public places and household gas detection and alarm.
