The classification of the latest version of the gas analyzer of Hengaode Instrument is based on the principle
The classification of the latest version of the gas analyzer of Hengaode Instrument is based on the principle
Gas detector is a kind of instrument and tool for gas leakage concentration detection, including: portable gas detector, handheld gas detector, fixed gas detector, online gas detector, etc. Gas sensors are mainly used to detect the types of gases present in the environment. Gas sensors are sensors used to detect the composition and content of gases.
It is generally believed that the definition of the gas sensor is based on the classification of the detection target, that is to say, any sensor used to detect the gas composition and concentration is called a gas sensor, regardless of whether it is a physical method or a chemical method. For example, sensors that detect gas flow are not considered gas sensors, but thermal conductivity gas analyzers are important gas sensors, although they sometimes use generally consistent detection principles.
classification
Semiconductor
It is manufactured using the principle of some metal oxide semiconductor materials, at a certain temperature, the conductivity changes with the change of the ambient gas composition. For example, the alcohol sensor is prepared by the principle that the resistance of tin dioxide will decrease sharply when it encounters alcohol gas at high temperature.
advantage
Semiconductor gas sensors can be effectively used to detect methane, ethane, propane, butane, alcohol, formaldehyde, carbon monoxide, carbon dioxide, ethylene, acetylene, vinyl chloride, styrene, acrylic acid and many other gases. In particular, this kind of sensor has low cost and is suitable for the demand of civil gas detection. The following semiconductor gas sensors are successful: methane (natural gas, biogas), alcohol, carbon monoxide (city gas), hydrogen sulfide, ammonia (including amines, hydrazines). High-quality sensors can meet the needs of industrial testing.
Disadvantages
The stability is poor, and it is greatly affected by the environment; in particular, the selectivity of each sensor is not unique, and the output parameters cannot be determined. Therefore, it should not be used in places where accurate measurement is required.
Combustion
This kind of sensor is to prepare a high temperature resistant catalyst layer on the surface of the platinum resistor. At a certain temperature, the combustible gas catalyzes combustion on its surface. The combustion is the temperature rise of the platinum resistor, and the resistance changes. function.
advantage
Catalytic combustion gas sensors selectively detect flammable gases: sensors that do not burn cannot respond. The catalytic combustion gas sensor has accurate measurement, fast response and long service life. The output of the sensor is directly related to the explosion hazard of the environment, and it is a leading sensor in the field of safety detection.
Disadvantages
In the flammable gas range, there is no selectivity. Work in dark fire, there is a risk of ignition and explosion. Most elemental organic vapors have a poisoning effect on the sensor.
Thermal conductivity
Each gas has its own specific thermal conductivity. When the thermal conductivity of two or more gases differs greatly, the thermal conductivity element can be used to distinguish the content of one of the components. Such sensors have been used sensorily for the detection of hydrogen, carbon dioxide, and high-concentration methane.
This gas sensor has a narrow application range and many limiting factors.
Electrochemical
A considerable portion of its flammable, toxic and harmful gases are electrochemically active and can be electrochemically oxidized or reduced. Using these reactions, the gas composition can be distinguished and the gas concentration can be detected. Electrochemical gas sensors are divided into many subcategories:
(1), galvanic gas sensor (also known as: gas battery gas sensor, also known as fuel cell gas sensor, also known as spontaneous battery gas sensor), their principle is the same as the dry battery we use, but The carbon manganese electrode of the battery is replaced by a gas electrode. Taking an oxygen sensor as an example, oxygen is reduced at the cathode and electrons flow to the anode through the ammeter, where the lead metal is oxidized. The magnitude of the current is directly related to the concentration of oxygen. This sensor can effectively detect oxygen, sulfur dioxide, chlorine, etc.
(2), constant potential electrolytic cell type gas sensor, this sensor is very effective for detecting reducing gas, its principle is different from the galvanic sensor, its electrochemical reaction occurs under the force of current, is a A true Coulomb analysis sensor. This sensor has been successfully used in the detection of carbon monoxide, hydrogen sulfide, hydrogen, ammonia, hydrazine, etc. It is the mainstream sensor for the detection of toxic and harmful gases.
classification
According to the way of use, it can be divided into desktop gas detector and handheld gas detector
According to the amount of gas that can be detected, it can be divided into a single gas detector and a variety of gas detectors
According to the principle of gas sensor, it can be divided into infrared gas detector, thermal magnetic gas detector, electrochemical gas detector, semiconductor gas detector, ultraviolet gas detector, etc.
principle
Take the 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 gas being measured. The infrared detector has a wide range of applications. It can analyze not only gas components but also solution components. It has high sensitivity, rapid response, continuous online indication, and can also form an adjustment system. The detection part of the infrared gas detector commonly used in the industry is composed 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 optical path simultaneously or alternately with a certain period through the light cutting plate. After the gas to be measured is introduced into the measurement chamber, light with a wavelength specific to the gas to be measured is absorbed, thereby reducing the luminous flux that enters the infrared receiving gas chamber through the optical path of the measurement chamber. The higher the gas concentration, the less the luminous flux entering the infrared receiving gas chamber; the luminous flux passing through the reference chamber is constant, and the luminous flux entering the infrared receiving gas chamber is also constant. Therefore, the higher the measured gas concentration, the greater the difference in luminous flux through the measurement chamber and the reference chamber. This difference in luminous flux is projected onto the infrared receiving gas chamber with an amplitude of a certain period of vibration. The receiving gas chamber is divided into two halves by a metal film with a thickness of several micrometers. The chamber is filled with the gas of the measured component with a relatively high concentration, which can absorb all the incident infrared rays within the absorption wavelength range, so that the pulsating luminous flux becomes The periodic change of temperature can then be converted into a change in pressure according to the gas state equation, and then detected with a capacitive sensor, which indicates the concentration of the measured gas after being amplified. In addition to capacitive sensors, quantum infrared sensors that directly detect infrared light can also be used. Infrared interference filters are used for wavelength selection and tunable lasers are used as light sources to form a brand-new all-solid infrared gas detector. This detector can use only one light source, a measurement room, and an infrared sensor to complete the measurement of gas concentration. In addition, if multiple optical filters with different wavelengths are used, the concentrations of various gases in the multi-component gas can be measured simultaneously.
use
The gas detector can detect a variety of gases such as hydrogen sulfide, carbon monoxide, oxygen, sulfur dioxide, phosphine, ammonia, nitrogen dioxide, hydrogen cyanide, chlorine, chlorine dioxide, ozone and combustible gases. It is widely used in petrochemical and coal , Metallurgy, chemical industry, municipal gas, environmental monitoring and other places on-site testing. It can meet the measurement needs of special occasions; can detect gas concentration or leak detection in tunnels, pipes, tanks, confined spaces, etc.
maintenance
1. Check the gas flow rate, usually 30 / h, if the flow rate is too large or too small, it will have a greater impact on the analyzer results
2. Replace the filter paper: stop the air pump and drain the filter tank
3. Check for air leakage in the gas circuit system. Whether the diaphragm of the sobbing pump is damaged, whether the sealing ring of the sampling probe is broken, whether the four-way valve and condensed steam are damaged
4. Cleaning the sampling probe, dredging the sampling hole pipeline
5. Check whether the condenser works normally, usually the temperature is adjusted within 3 degrees Celsius
6. Check the measuring room to see if it is dirty and clean it in time.
Purchase method
1) Confirm the gas type and concentration range to be detected:
The gas types encountered in each production department are different. When choosing a gas detector, all possible situations must be considered. If methane and other less toxic alkanes are predominant, the choice of LEL detector is undoubtedly the most suitable. This is not only because the LEL detector is simple in principle and widely used, but also has the characteristics of easy maintenance and calibration. If there are toxic gases such as carbon monoxide and hydrogen sulfide, a specific gas detector must be selected first to ensure worker safety. If it is more organic toxic and harmful gases, considering the low concentration that may cause personnel poisoning, such as aromatic hydrocarbons, halogenated hydrocarbons, ammonia (amines), ethers, alcohols, fats, etc., you should choose Ionization detector, and never use the LEL detector to deal with, because this may cause personal injury or death.
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