The working principle of hydrogen sulfide H2S gas detector mainly relies on electrochemical, optical or semiconductor sensing technologies. The following is a detailed description of the common principles:
Electrochemical sensors are the most commonly used, and their principle is to detect the concentration of H₂S by using electrochemical reactions. There is an electrolyte (such as an acidic solution) and three electrodes (working electrode, counter electrode and reference electrode) inside the sensor.
1.Work process:
(1).H₂S gas naturally diffuses into the sensor through the breathable membrane.
(2).Oxidation reaction occurs on the working electrode
(3). A reduction reaction occurs on the counter electrode (usually oxygen reduction)
(4).The generated current is directly proportional to the H₂S concentration and is converted into a concentration reading through the circuit.
2.Features
(1).It can detect H₂S concentrations at the ppm (parts per million) or even ppb (parts per billion) level, and is suitable for monitoring low-concentration toxic gases (such as industrial safety and environmental monitoring).
(2).It has a selective response to H₂S. By optimizing the electrode material and electrolyte, the interference of other gases (such as CO, SO₂) can be reduced.
(3).The output current has a good linear relationship with the H₂S concentration, which is convenient for signal processing and calibration.
3..Principle of semiconductor sensors: After the surface of metal oxides (such as SnO₂) adsorbs H₂S, the resistance changes.
H₂S reacts with semiconductor materials, releasing electrons and causing a decrease in resistance. The concentration can be calculated by measuring the resistance change through a circuit. It has low cost and long service life, but is easily affected by temperature and humidity and requires regular calibration.
4.Optical sensors (such as NDIR or colorimetric method
H₂S molecules have absorption characteristics at specific infrared wavelengths (such as ~3.7 μm), and the concentration is calculated by measuring the attenuation of light intensity. The gas reacts with chemical reagents (such as lead acetate) to produce color changes (such as black lead sulfide), and the depth of the color is detected by a photosensitive element. Its characteristic is strong anti-interference ability, but the cost is relatively high, and it is mostly used for fixed industrial inspection.