What are the working principles of common gas detectors?
(1) The combustible gas detector adopts a new generation of low-power and high anti-interference carrier catalytic sensor. It forms a detection bridge with two fixed resistors. When combustible gases in the air diffuse onto the surface of the detection sensor, they rapidly undergo flameless combustion under the action of the catalyst on the sensor surface, generating reaction heat that increases the platinum wire resistance value of the sensor. The detection bridge outputs a differential pressure signal. The magnitude of this voltage signal is directly proportional to the concentration of combustible gases. After amplification, it performs voltage current conversion and converts the percentage content (% LEL) within the lower explosive limit of flammable gases into a 4-20mA standard signal output.
(2) The oxygen detector applies the principle of the galvanic primary cell, which is constructed by installing an anode (lead) and a cathode (silver) inside the primary cell, separated from the outside by a thin film. When oxygen-containing gases in the air pass through this thin film and reach the cathode, oxidation-reduction reactions occur. At this time, the sensor will have a mV level voltage output proportional to the oxygen concentration. After amplification, this voltage signal is converted into a voltage current conversion and the percentage of oxygen (0-30%) is converted into a 4-20mA standard signal output.
(3) The toxic and harmful gas detector adopts the world's advanced imported electrochemical sensor, which applies the principle of controlled potential electrolysis. Its structure is to place three electrodes in the electrolytic cell, namely the working electrode, the counter electrode, and the reference electrode, and apply a certain polarization voltage. By replacing the sensor for different gases and changing the polarization voltage value, different toxic and harmful gases can be measured.
The measured gas passes through the thin film and reaches the working electrode, where an oxidation-reduction reaction occurs. At this time, the sensor will output a small current, which is directly proportional to the concentration of toxic and harmful gases. This current signal is sampled and converted into voltage, which is then amplified and converted into voltage and current. The content (ppm value) within the detection range of toxic and harmful gases is converted into a 4-20mA standard signal output.
The organic volatile compounds are detected using the world's high-quality photoionization gas sensor (PID), which utilizes the principle of photoionization gas for gas detection. Specifically, it is to use ultraviolet light generated by an ion lamp to irradiate/bombard the target gas. After the target gas absorbs enough ultraviolet light energy, it will be ionized. By detecting the small current generated by the ionization of the gas, the concentration of the target gas can be detected.
(4) The carbon dioxide detector adopts the world's advanced infrared principle sensor, which uses the physical properties of infrared to measure. It includes an optical system, detection elements, and photoelectric detection elements. Optical systems can be divided into two categories based on their structures: transmissive and reflective. Detection components can be divided into thermosensitive detection components and photoelectric detection components according to their working principles. The most commonly used thermistor is thermistor. When a thermistor is exposed to infrared radiation, its temperature increases and its resistance changes, which is then converted into an electrical signal output through a conversion circuit.
