What is a gas analyzer

 

Gas analyzer is a process analysis instrument for measuring gas composition. In many production processes, especially in the production process with chemical reaction, it is often not enough to carry out automatic control only according to physical parameters such as temperature, pressure and flow. Due to the wide variety of gases to be analyzed and the diversity of analysis principles, there are many kinds of gas analyzers. Thermal conductivity gas analyzer, electrochemical gas analyzer and infrared absorption analyzer are commonly used.

 

Principle of gas analyzer

 

Gas sensors are mainly used to detect the types of gases in the environment. Gas sensors are sensors used to detect the composition and content of gases. The gas sensor is generally used for gas detection, that is, whether it is based on the physical method or chemical method, that is to say, it is used for gas detection. 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.

 

 

Types of gas analyzers

 

Thermal conductivity

 

A physical gas analyzer. According to the principle that different gases have different thermal conductivity, it calculates the content of some components by measuring the thermal conductivity of mixed gases. This kind of analytical instrument is simple, reliable and applicable to many kinds of gases. It is a basic analytical instrument. However, it is difficult to directly measure the thermal conductivity of gas, so in fact, the change of thermal conductivity of gas is often converted into the change of resistance, and then measured by electric bridge. The thermal sensitive elements of thermal conductivity gas analyzer mainly include semiconductor sensitive elements and metal resistance wires. Semiconductor sensor has small volume, small thermal inertia and large resistance temperature coefficient, so it has high sensitivity and small time lag. The bead metal oxide is sintered on the platinum coil as the sensing element, and then the same platinum coil with equal internal resistance and calorific value is wound with a material that does not react to the gas as the compensation element. These two elements form a bridge circuit as two arms, that is, the measuring circuit. When the semiconductor metal oxide sensing element adsorbs the measured gas, the conductivity and thermal conductivity change, and the heat dissipation state of the element also changes. The temperature change of the element changes the resistance of the platinum coil, and the bridge has an unbalanced voltage output, according to which the gas concentration can be detected. Thermal conductivity gas analyzer has a wide range of applications. In addition to analyzing the contents of hydrogen, ammonia, carbon dioxide, sulfur dioxide and low concentration combustible gases, it can also be used as a detector in chromatographic analyzer to analyze other components.

 

Thermomagnetic

 

Thermomagnetic oxygen analyzer

 

The principle is to determine the oxygen content in flue gas by using the physical property that the magnetic susceptibility of oxygen in flue gas components is particularly high. Oxygen is a paramagnetic gas (the gas that can be attracted by the magnetic field is called paramagnetic gas), which is attracted in the uneven magnetic field and flows to the place with strong magnetic field. There is a heating wire, which increases the temperature of oxygen and decreases the magnetic susceptibility, so the attraction of the magnetic field decreases, and the magnetic field is pushed out by the unheated oxygen molecules with high magnetic susceptibility, resulting in the phenomenon of "thermal magnetic convection" or "magnetic wind". Under certain gas sample pressure, temperature and flow, the oxygen content in the gas sample can be measured by measuring the magnetic wind. As the thermistor (platinum wire) acts as both the two bridge arm resistors of the unbalanced bridge and the heating resistance wire, there is a temperature gradient under the action of magnetic wind, that is, the temperature of the bridge arm on the inlet side is lower than that on the outlet side. The unbalanced bridge will output the corresponding voltage value with the different oxygen content in the gas sample.

 

Thermomagnetic oxygen analyzer has the advantages of simple structure, easy manufacture and adjustment.

 

Electrochemical formula

 

A chemical gas analysis instrument. It measures the gas composition according to the change of ion quantity or current caused by chemical reaction. In order to improve selectivity, prevent contamination on the surface of measuring electrode and maintain the performance of electrolyte, diaphragm structure is generally adopted. There are two kinds of commonly used electrochemical analyzers: constant potential electrolytic analyzer and galvanni battery analyzer. The working principle of constant potential electrolytic analyzer is to apply a specific potential on the electrode, and the measured gas will produce electrolytic effect on the electrode surface. As long as the potential added to the electrode is measured, the unique electrolytic potential of the measured gas can be determined, so that the instrument has the ability to select and identify the measured gas. The galvanni battery analyzer electrolyzes the measured gas diffused into the electrolyte through the diaphragm. The concentration of the measured gas can be determined by measuring the formed electrolytic current. The internal voltage on the electrode surface is changed by selecting different electrode materials and electrolyte, so as to realize the selectivity of gases with different electrolytic potentials.

 

Infrared absorption type

 

An analytical instrument that works according to the selective absorption characteristics of different component gases to infrared rays of different wavelengths. Measuring this absorption spectrum can distinguish the type of gas; Measuring the absorption intensity can determine the concentration of the measured gas. The infrared analyzer has a wide range of application. It can analyze not only gas components, but also solution components. It has high sensitivity, rapid response, online continuous indication and adjustment system. The detection part of infrared gas analyzer commonly used in 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 light path simultaneously or alternately in a certain period through the light cutting plate. After the measured gas is introduced into the measuring chamber, the light with the unique wavelength of the measured gas is absorbed, so that the luminous flux entering the infrared receiving chamber through the optical path of the measuring chamber is reduced. The higher the gas concentration, the less the luminous flux entering the infrared receiving chamber; The luminous flux passing through the reference chamber is certain, and the luminous flux entering the infrared receiving chamber is also certain. Therefore, the higher the concentration of the measured gas, the greater the difference in luminous flux between the measuring chamber and the reference chamber. The luminous flux difference is projected to the infrared receiving chamber with the amplitude of periodic vibration. The receiving gas chamber is divided into two parts by a metal film several microns thick. The chamber is sealed with a high concentration of the measured component gas. Within the absorption wavelength range, it can absorb all the emitted infrared rays, so as to change the pulsating luminous flux into the periodic change of temperature. Then, the change of temperature can be converted into the change of pressure according to the gas equation, and then detected by a capacitive sensor. After amplification, the concentration of the measured gas can be indicated. In addition to the capacitive sensor, a quantum infrared sensor that can directly detect infrared can also be used. A new all solid infrared gas analyzer is formed by using infrared interference filter for wavelength selection and adjustable laser as light source. The analyzer can measure the gas concentration with only one light source, one measuring room and one infrared sensor. In addition, if filter discs with multiple different wavelengths are used, the concentrations of various gases in multi-component gases can be measured at the same time.

 

Similar to the principle of infrared analyzer are ultraviolet analyzer and photoelectric colorimetric analyzer, which are also widely used in industry.

 

Non dispersive infrared analysis

 

Non dispersive infrared analysis combines two non dispersive spectral analysis technologies: narrow-band filter and gas filter correlation method, which is suitable for different measurement range requirements of gas.

 

The filter correlation method can measure low range gas and effectively avoid cross interference. This unique technology can eliminate the cross interference of weak absorption gas such as CO and high absorption gas CO2.

 

The infrared light emitted by the heat source is filtered by the rotary filter, resulting in a series of pulse signals directly passing through the unit containing sample gas. When the filter wheel rotates, the solid-state detector reflects the signal change, amplifies and displays the signal.

 

To sum up, do you know more about the gas analyzer? If you have any questions, please leave a message at any time. See you next time.