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Classification and Working Principle of Gas Monitoring Sensors

Gas monitoring sensors are essential tools used in various industries for detecting the presence and concentration of different gases. These sensors come in multiple types, each based on a unique principle of operation. The main categories include semiconductor sensors (resistive and non-resistive), insulator-based sensors (contact combustion and capacitive), electrochemical sensors (potentiostatic and galvanic), as well as infrared absorption, quartz oscillation, optical fiber, thermal conductivity, surface acoustic wave, and gas chromatography types. Resistive semiconductor gas sensors work by measuring changes in the resistance of the semiconductor material when it comes into contact with a specific gas. Non-resistive semiconductor sensors, on the other hand, rely on the adsorption and chemical reaction of the gas on the sensor surface, which alters its electrical properties. These changes can be measured directly or indirectly to determine gas concentration. Contact combustion gas sensors operate based on the heat generated when a flammable gas reacts on a catalytic surface. This heat causes a temperature increase, which affects the conductance of a noble metal electrode. Unlike some other sensor types, these are less influenced by environmental humidity. Capacitive gas sensors function by detecting changes in the dielectric constant of a sensitive material when exposed to a gas. This change results in a measurable variation in capacitance, allowing for gas detection. Electrochemical gas sensors utilize the difference in chemical potential between two electrodes—one acting as a working electrode that interacts with the gas, and the other serving as a reference electrode. These sensors typically use either a potentiostatic electrolysis method or a galvanic cell method. They can have liquid or solid electrolytes, with liquid electrolytes further divided into potential and current types. Each type of gas sensor has its own advantages and limitations, making them suitable for different applications depending on the environment, required sensitivity, and target gas.