Take a common infrared gas detector as an example to illustrate the principle of the gas detector:
Measuring this absorption spectrum can identify the type of gas; measuring the absorption intensity can determine the concentration of the measured gas. The infrared detector has a wide range of use, not only can analyze the gas composition, but also the solution composition, and has high sensitivity, rapid response, continuous online indication, and can also form a regulating system. The detection part of the infrared gas detector commonly used in industry consists of two parallel optical systems with the same structure.
One is the measurement room and the other is the reference room. The two chambers open and close the light path simultaneously or alternately in a certain period through the light-cutting plate.
After the gas to be measured is introduced into the measurement chamber, the light with the wavelength unique to the gas to be measured is absorbed, thereby reducing the luminous flux that passes through the optical path of the measurement chamber and enters the infrared receiving gas chamber. The higher the gas concentration, the less luminous flux entering the infrared receiving chamber; while the luminous flux passing through the reference chamber is constant, and the luminous flux entering the infrared receiving chamber is also constant.
Therefore, the higher the concentration of the measured gas, the greater the difference in luminous flux passing through the measuring chamber and the reference chamber. This difference in luminous flux is projected to the infrared receiving air cell with the amplitude of a certain periodic vibration. The receiving gas chamber is divided into two halves by a metal film with a thickness of several microns, and the gas of the measured component with a large concentration is sealed in the chamber, which can absorb all the incoming infrared rays in the absorption wavelength range, so that the pulsating light flux becomes The periodic change of temperature can be converted into a pressure change according to the gas state equation, and then detected by a capacitive sensor, and the concentration of the measured gas is indicated after amplification. In addition to capacitive sensors, quantum infrared sensors that directly detect infrared light can also be used, and infrared interference filters are used for wavelength selection and a tunable laser is used as a light source to form a new all-solid-state infrared gas detector. This detector only needs a light source, a measuring chamber, and an infrared sensor to complete the gas concentration measurement. In addition, if a plurality of filter discs with different wavelengths are used, the concentration of each gas in the multi-component gas can be measured simultaneously.
