Since the beginning of the 20th century, Fourier transform infrared (FT-IR) spectroscopy has been a widely used research tool in the fields of chemistry, life sciences, and materials science. In addition to providing molecular structure and composition information, it can also control the reaction dynamics process and investigate the interaction of substances at different temperatures.

From the late 1960 s to the early 1970 s, W.M. Gabriel simultaneously developed real-time circuits to combat intersection interference and reduce the amount of estimation errors (with small errors). The introduction of data processing in Cartesian coordinates made the method rapidly popularized.

Along with the computer hardware equipment more and more advanced and easy to obtain our country also gradually carried on the application, infrared spectroscopy technology in agriculture, environmental protection and medicine and so on many fields obtained the widespread use. Fourier infrared spectrometer in the domestic development and use of the situation relative to developed countries, the start is still relatively late.

What is the working principle of the infrared spectrometer? The infrared spectrometer is an instrument that analyzes the molecular structure and chemical composition of substances by using the absorption characteristics of infrared radiation of different wavelengths. Infrared spectrometer usually consists of light source, monochromator, detector and computer processing information system. According to the different spectroscopic device, it is divided into dispersion type and interference type. For the dispersive dual-path optical zero-balance infrared spectrophotometer, when the sample absorbs a certain frequency of infrared radiation, the vibration energy level of the molecule transitions, and the light of the corresponding frequency in the transmitted beam is weakened, resulting in a difference in the intensity of the corresponding radiation between the reference light path and the sample light path, so as to obtain the infrared spectrum of the measured sample.

The infrared part of the electromagnetic spectrum can be divided into near-infrared, mid-infrared and far-infrared light according to its relationship with the visible spectrum. Far-infrared light (about 400-10 cm-1) is adjacent to microwaves and has low energy and can be used for rotational spectroscopy. Mid-infrared light (about 4000-400 cm-1) can be used to study the base vibration and related rotation-vibration structures. Higher energy near infrared light (14000-4000 cm-1) can stimulate overtones and harmonic vibrations. The working principle of infrared spectroscopy is that chemical bonds have different frequencies due to different vibration energy levels. The resonance frequency, or vibrational frequency, depends on the shape of the molecular equipotential surfaces, the atomic mass, and the resulting associated vibrational coupling. In order for the vibrational mode of the molecule to be active in the infrared, there must be a permanent dipolar change. Specifically, in the Bonn-Oppenheimer harmonic oscillator approximation, for example, when the molecular Hamiltonian corresponding to the electronic ground state can be approximated by the harmonic oscillator near the equilibrium state of the molecular geometry, the natural oscillation mode determined by the potential surface of the molecular electronic energy ground state determines the resonance frequency. However, the resonance frequency is related to the strength of the bond and the atomic mass at both ends of the bond after a first approximation. In this way, the vibration frequency can be associated with a particular key type. Simple diatomic molecules have only one type of bond, which is stretching. More complex molecules may have many bonds, and vibrations may appear conjugated, resulting in infrared absorption at certain characteristic frequencies that can be associated with chemical groups. The CH2 group, often found in organic compounds, can vibrate in six ways: "symmetrical and asymmetrical stretching", "scissor oscillation", "left and right oscillation", "up and down oscillation" and "torsion pendulum.

At present, there are two mainstream flue gas analyzers on the market, one is the electrochemical working principle, and the other is the infrared working principle. At present, portable flue gas analyzers on the market usually combine these two principles. The following is an introduction to the working principles of these two flue gas analyzers:

The working principle of the electrochemical gas sensor: the gas to be measured enters the sensor chamber after dust removal and dehumidification, and enters the electrolytic cell through the permeable membrane, so that the gas diffused and absorbed in the electrolyte undergoes potential electrolysis under the specified oxidation potential, and the consumption The electrolytic current used calculates the concentration of its gas. A working electrode, a counter electrode, and a reference electrode were mounted in a cylindrical cell made of plastic, filled with an electrolyte between the electrodes, and a separator made of porous tetrafluoroethylene was encapsulated on top. The preamplifier is connected to the sensor electrodes, and a certain potential is applied between the electrodes to make the sensor in a working state. The gas oxidation or reduction reaction occurs at the working electrode in the electrolyte, and the reduction or oxidation reaction occurs at the counter electrode, and the equilibrium potential of the electrode changes, and the change value is proportional to the gas concentration. SO2, NO, NO2, CO, H2S and other gases can be measured, but the sensitivity of these gas sensors is different. The order of sensitivity from high to low is H2S, NO, NO2, SO2, CO, and the response time is generally several seconds to tens of seconds, generally less than 1min; Their life span is only half a year for the short one, and 2 or 3 years for the long one, which requires continuous maintenance.

Fourier infrared analyzer works: based on the characteristics of a variety of gases with selective absorption of infrared radiation, infrared is absorbed by a component of the gas, the radiation can be partially converted into heat energy, the gas temperature, by measuring the gas temperature change or constant volume of gas pressure changes, you can know the content of this component in the gas. It can analyze a wide range of objects (such as carbon monoxide, carbon dioxide, methane, acetylene, various hydrocarbons, ethanol and steam content), high sensitivity, wide range, fast response speed. Infrared analyzer is an analytical method based on the selective absorption of infrared light by the measured medium, which belongs to the molecular absorption spectrum analysis method. The infrared rays pass through the measured gas contained in a container of a certain length, and then the measured gas concentration is measured by measuring the intensity of the infrared radiation after passing through the gas. Based on the life of the Fourier infrared flue gas analyzer is generally up to 10 years.

It is worth mentioning that because the molecules of oxygen and nitrogen are not in the infrared band in the infrared spectrum, they cannot absorb infrared rays. Therefore, the infrared flue gas analyzer based on Fourier cannot directly measure oxygen, and the flue gas monitoring equipment must judge whether the pollutant emission is completely burned by detecting the oxygen content. Therefore, an additional oxygen sensor must be added to the Fourier flue gas analyzer to detect the oxygen concentration in the gas.

Fourier infrared is the best type of flue gas monitoring equipment on the market, but it needs to heat the flue gas180degree, so the oxygen sensor with it also needs to have high temperature resistance characteristics, agentO2S-FR-T2-18C/B/AIs a zirconia oxygen sensor, the product usesM18 x 1.5mmThe threaded mounting housing adopts a sturdy stainless steel structure, which can cope with extreme temperature levels (from-100°CTo250°C). This makes it very suitable for industrial coal/Oil/Gas/Combustion control in biomass boiler, Fourier infrared flue gas analyzer continuous emission monitoring system.

In addition, the zirconia oxygen sensor can be matched with a OXY-LC interface transmission board, and can output standard industrial 4-20mA, 0-10V or RS485 signals.

      1. RS485 communication can completely control the operation of the sensor and obtain all useful information of the sensor including error diagnosis.

The sensor responds quickly and can obtain a stable oxygen concentration output value through filtering.

3. Can be calibrated in air (20.7% oxygen), or other environment with known oxygen concentration.

4. Adjustable communication settings, including the ability to change the slave address of the interface, allowing communication of up to 32 interfaces on the same bus. It can be perfectly used in the field of multi-oxygen reading.

5. There are reverse voltage and instantaneous overvoltage protection on the power supply connection line.

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