The gas sensor is the core component of the gas detector, which converts the change in gas concentration into a corresponding electrical signal. There are several common gas sensors such as catalytic combustion, semiconductor, infrared, photocall ionization (PID), and electrochemical. The working principles of the different classifications are described below.
A catalytic combustion gas sensor is currently the most commonly used low-cost combustible gas sensor. It has a pair of small internal "beads" made of platinum wire coils wrapped with the ceramic base material, one of which is a sensitive "bead" as a detection element. Its surface is covered with a layer of catalyst, which will react with all the presence of combustible gases. The other is an emotional "bead" that does not react with any gas and is only used as a compensating element for external temperature or humidity variations.
The platinum wire coil is heated to 450 ℃ ~ 500 ℃ high in normal operation. When in contact with combustible gases, the detection element surface catalytic combustion reaction, the temperature increases, the internal resistance of the platinum wire also increased accordingly, through the Wheatstone bridge can accurately measure the resistance of the detection element changes, to calculate the concentration of the detected gas.
Semiconductor gas sensors are often used to detect low concentrations of combustible and toxic gases. Its gas-sensitive element is a thin metal oxide film deposited on a silicon wafer. When the detection gas comes into contact with the metal oxide, it will be adsorbed on its surface, causing the resistance of the metal oxide to change. This change in resistance is related to the change in gas concentration. Usually, the surface of the semiconductor sensor is heated to a constant temperature between 200°C and 250°C to increase the reaction rate and reduce the effect of ambient temperature changes.
An infrared gas sensor is mainly used to detect combustible and carbon dioxide gas. Compared with catalytic combustion gas sensors, it has the advantages of better stability, high accuracy, strong anti-interference ability, no poisoning, suitable for harsh environments, less maintenance, and long life, etc. It is usually regarded as a high-end product for detecting combustible gases; due to the price, it is not as widely used as catalytic combustion gas sensors, but the price gap between them is, however, with the continuous progress and maturity of infrared sensor manufacturing technology, the price gap between the two is narrowing. The common infrared gas sensors are point type and open circuit type.
Point-type infrared gas sensors consist of an infrared source, an optical focusing mirror, a sampling gas chamber, and a pyroelectric sensor. When the infrared light from the infrared source passes through the sampling gas chamber, the infrared light of a specific wavelength is absorbed by the detection gas in the chamber.
The open-circuit infrared gas sensor consists of a transmitter and a receiver, which must be installed in pairs. The transmitter emits a beam of infrared light to the receiver, and when the gas is present, the infrared light of a specific wavelength in the beam is absorbed by the gas. The measurement unit of an open-circuit infrared gas detector is LEL.m, which is the overall gas concentration in the optical path multiplied by the distance.
Photo Ionization Detector (PID) type gas sensor can detect the concentration of volatile organic compounds (VOC) and other toxic gases at very low concentrations (ppm or even ppb level).PID type gas sensor uses the principle of photoionization of gases to detect gases. It uses an ultraviolet (UV) light source to break the organic material into positive and negative ions that can be detected by the detector (ionization). The detector detects the ionized gas charge and converts it into a current signal, amplified and displayed as the ppm concentration value of the gas. After detection, the ion will be reverted to the original gas or vapor. PID sensor is a non-breaking sensor. It will not "burn" or permanently change the gas to be measured so that the gas detected by PID can still be collected for further measurement.
Electrochemical gas sensor (Electrochemical gas sensor) is irreplaceable in detecting toxic and hazardous gases. An electrochemical gas sensor is composed of electrolyte, electrode, and filter. By selecting the appropriate voltage, electrolyte, and electrode material, the measured gas reacts chemically on the electrode surface and generates a microcurrent proportional to the gas concentration.
Hot News
