What are the characteristics of the different principle CO2 sensors?
The carbon dioxide sensor is a component specially used to detect the concentration of CO2 in various environments. Common carbon dioxide sensors mainly include the following types:
Principle of Thermal Conductivity
The gas sensor based on the principle of thermal conductivity is a gas sensor based on the principle that different gases have different thermal conductivity under the same conditions. Under certain conditions, changes in the concentration or composition of the measured gas will cause changes in the thermal conductivity of the gas sensor's working environment, which will cause changes in the surface temperature of the sensor, and further lead to changes in the resistance of the sensor's temperature-sensing element. The detection of gas concentration is realized by measuring the change of the temperature sensing resistance of the sensor. This kind of sensor is generally greatly affected by the ambient temperature, so it can only be distinguished by gas grade range.
Used to detect carbon dioxide gas on industrial sites and can be used in anaerobic or hypoxic environments.
Principle of Solid Electrolyte
Solid electrolyte gas sensor is a gas sensor based on the principle of solid electrolyte battery. Under certain temperature conditions, when the sensor is placed in the atmosphere to be measured, the electrode reaction of the solid electrolyte battery occurs, and the potential difference between the sensitive electrode of the sensor and the reference electrode conforms to the Nernst equation, and the gas concentration is detected by the voltage signal output by the two stages of the sensor . The solid electrolyte has good linearity within a certain concentration range, and is suitable for gas detection in various fields of civil, agricultural and industrial fields.
Used in air quality control systems, fermentation process control systems and greenhouses and other places.
NDIR Infrared Principle
Infrared carbon dioxide sensor is an optical sensor mainly composed of infrared light source, optical path, infrared detector, circuit and software algorithm. Its working principle is based on the selective absorption characteristics of near-infrared spectra of different gas molecules, and uses the relationship between gas concentration and absorption intensity (Lambert-Beer law) to identify gas components and determine their concentrations. Infrared carbon dioxide sensor has very good selectivity to CO2, long life and high precision. It is a type of sensor widely recognized by the market in carbon dioxide monitoring.
Infrared carbon dioxide sensors are divided into single-channel and dual-channel. Single-channel means that a photosensitive device and a narrow-band filter are integrated inside the infrared detector to allow light with a central wavelength of 4.26 μm to pass through while reflecting or attenuating light of other wavelengths. Dual-channel is to integrate a reference channel on the basis of a single-channel infrared detector, and integrate 2 photosensitive devices and 2 narrow-band filters inside. One of the channels allows light with a center wavelength of 4.26um to pass through, while the other channel staggers a specific wavelength (commonly used CO2, CO, SO2, and NO have no absorption), and the signal is relatively stable and can be used as a reference channel.
In carbon dioxide detection in non-industrial fields, Winsen has single-channel civil carbon dioxide sensor products and dual-channel commercial carbon dioxide sensor products.
Single-channel infrared carbon dioxide sensors include MH-Z19C, MH-Z14A, etc. MH-Z19 series are widely used in household products such as detectors, fresh air systems, and intelligent air conditioners; MH-Z14 series are mainly used in building automation and other places.