first, the importance and necessity of the application of dust on-line monitor. The process medium of TRT unit is blast furnace gas, and its working principle is to use the pressure energy and heat energy of blast furnace gas to drive the unit to generate electricity. However, blast furnace gas has a high dust content and can only be used after dust removal. Usually, there are two ways of blast furnace gas dust removal: dry method and wet method. The dust content of blast furnace gas has a vital influence on the safe operation of blades of TRT unit. Usually, TRT unit requires the dust content of gas to be <: 5 mg/m, too much dust content will cause serious wear and tear to the blades of TRT unit, which will seriously affect the safe operation of the unit. However, the bag of blast furnace gas dust collector will be damaged and the dust removal effect will be reduced due to long-term work, so the dust content of blast furnace gas entering the unit will exceed the standard, which means that the unsafe working conditions of TRT unit due to the long-term operation of bag dust collector will also occur at any time. In order to ensure the safety of TRT unit, it is necessary to know the dust content of blast furnace gas, the working state of blast furnace gas dust collector, the operating environment of TRT unit and the working state of TRT unit in time, so it is necessary to control it in TRT unit. 2. At present, several methods of on-line dust monitor The measurement of dust mass content belongs to the category of gas-solid two-phase flow, which becomes a difficult measurement field due to the inherent complexity of multiphase flow. Through the continuous efforts of scientists all over the world, traditionally, there are mainly two kinds of measurement technologies: optical technology and triboelectricity technology. However, due to the technical constraints and the influence of many factors, the measurement results have not been able to completely meet the actual measurement needs. Optical technology products need frequent cleaning and maintenance because their optical lenses are easy to be polluted, and the maintenance workload is heavy; The measurement results are also affected by factors such as dust color and temperature change, and low-content dust cannot be measured. Triboelectric sensing technology, which uses the friction between dust and sensor probe to generate static electricity to measure the dust content, is a contact measurement method. Due to many factors, such as: ① adhesion, agglutination, condensation, moisture and drying of dust on the probe surface. ② Corrosion, high temperature, and metallicity of metal E.. ③ Changes in velocity, size and distribution of dust. They all affect the friction effect, leading to a fatal impact on the measurement results, so it is impossible to measure quantitatively and accurately. Moreover, it is difficult to install, debug, calibrate and maintain, and the zero drift is serious. Therefore, at present, it is usually only used for qualitative rough measurement (and it must work in an "ideal" environment without the influence of the above factors) or simply to detect whether there is dust, and there is no stable and direct data output in mg/m. Due to the limitation of sensing principle, even the triboelectric products of developed countries such as the United States and Germany cannot completely overcome the above problems. There have also been companies (such as Australian Plateau Company) that used triboelectric technology to accurately measure dust content. Because probe purging devices and other anti-interference measures must be added, the measurement system is complicated and expensive. At present, all the influencing factors have not been completely overcome, and the measurement results are unreliable. EM171C dust on-line monitor of American Inpro (Felson) Company is the latest technology product in the world at present. It uses the proprietary charge induction technology to measure the dust mass content, which completely solves the difficulties that could not be overcome by using "optical" or "triboelectric" technology products in the past, and is rapidly eliminating the above technology products in markets all over the world. EM171C on-line dust monitor of Fisher Company of the United States adopts the non-contact "charge induction" measurement method, as shown in the figure: when particles flow near the probe inserted into the pipeline or flue, small electrical signals are induced in the probe based on the electrons (i.e. charges) inside the particles. The digital signal processor converts the induction signal into an absolute output value linearly proportional to the particle mass content. It is based on the principle of quantum physics, that is, any substance (such as dust) has a charge (very little, usually picoampere level) inside. When the dust passes near the sensor probe, the "charge induction" sensor probe of the EM171C dust on-line monitor can induce an electrical signal at the sensor probe hood according to the charge inside the dust passing near it (not depending on the contact between the dust and the probe). This electrical signal The dust content (Illg／Ill) can be accurately measured by amplifying and calculating this electrical signal step by step. Therefore, the measurement results of charge induction technology are not affected by the changes of probe surface adhesion, agglutination, condensation, moisture, drying, dust flow rate, size and distribution, and do not need maintenance. 3. Comparison between charge induction and triboelectric technology Compared with the traditional triboelectric detection technology, the most fundamental difference of charge induction technology is that it induces related electrical signals in the probe through the electrons (charges) in the particles near the probe, which is a non-contact measurement method, and there is a direct correspondence between the signals and the particle mass content; Triboelectric technology is a contact measurement method, which generates related electrical signals in the probe through the collision and friction between particles and the probe, and there is no direct correspondence between the signals and the particle mass content. Because the triboelectric technology relies on contact measurement, it can't add a protective layer on the surface of the probe to isolate the particles/gas from the sensor core of the probe, resulting in the measurement value being affected by many factors such as particle accumulation, condensation, moisture, drying, particle characteristics, particle speed, etc., it can't complete accurate and reliable measurement, and the workload of installation, debugging, calibration and maintenance is heavy, so it is gradually being eliminated. Because the charge induction technology is a non-contact measurement, it completely avoids the influence of the above factors and other factors, and has great advancement, and directly outputs the measured value in Da (mg/m). Charge induction technology has higher resolution and accuracy, and can measure lower content. It can be used in wet or dry environment, and is not affected by particle characteristics and speed, particle accumulation on the probe, and does not need field calibration and maintenance. The main features of triboelectric technology are shown in the table below. The main features of surface charge induction and triboelectricity technology are compared with the main features of charge induction and probe protection technology and triboelectricity conduction technology. Charge induction and probe protection triboelectricity conduction probe isolation protection non-isolation protection measurement mode Non-contact (probe metal conductive layer does not have to be in direct contact with particles) Contact (probe metal conductive layer must be in direct contact with particles) The probe electric signal is generated through non-contact induction mode. According to the particle charge and particle distribution, an electrical signal is directly induced in the probe. Through the contact and impact between the particles and the metal layer of the probe, the charge is conducted into the probe to generate an electrical signal. Conductive particles can be used to measure wet gas dust that can't be measured, and the mass content can be measured accurately and continuously in the unit that can't measure the measurement result. The measurement result is in pA(mg/m 3) and the signal is output continuously for 4-21 Ma. Usually, only qualitative and rough measurements can be made, but the mass content can't be measured. There is no output signal in mg/m 3, and only the voltage/current/percentage signal without measurement unit is output (unless it is calibrated by isokinetic sampling method in the field). The linear measurement signal is directly linear with the mass content, and the indirect linear relationship between the measurement signal and the mass content is high in resolution and low in content, and the content can be measured as low as 1.1 mg/m 3. It is not possible to measure and separate the basic value (trough value) and peak value (wave peak value) of dust content at the same time for the pulse jet bag dust removal system. It is impossible to measure and separate the basic value (trough value) and peak value (wave peak value) of dust content at the same time. Low content can be measured, and the content as low as 1.1 mg/m 3 can be measured cannot