In the treatment of mine water hazards, ground pre-grouting technology has been widely used. Before the coal mine shaft excavation, in order to ensure the smooth excavation of the wellbore and prevent serious accidents such as flooding and flooding, the ground pre-grouting method often simultaneously protects the bedrock and the surface soil layer of the wellbore with the freezing construction method. A waterproof curtain is formed around the wellbore to ensure the safety of the wellbore. In the ground pre-grouting construction, the injection volume of grouting slurry is one of the important parameters for evaluating the effect of surface pre-grouting. The measurement is still based on the calculation of the product of pump volume and grouting time as the grouting volume. To calculate roughly. Since the working status of the injection pump, the viscosity of the grouting slurry, and the human factors of the metering personnel all affect the measurement result of the grouting amount, the use of an instrument capable of automatically measuring the grouting amount not only can improve the measurement. Accuracy can also reduce the labor intensity of workers and improve work efficiency. So far, there are 60 types of flow meters available for industrial use. The reason why so many varieties are so far is that they have not found a flow test instrument that can be applied to any fluid type, any range, any flow state, and any use conditions. Each of these flow meters has its own specific scope of application and also has its limitations. Flow measurement instrument according to the principle of measurement divided into mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, principles of atomic physics and so on. According to the current most popular and most extensive classification method, it can be divided into: differential pressure flowmeter, volumetric flowmeter, floater flowmeter, turbine flowmeter, electromagnetic flowmeter, fluid vibrating flowmeter, ultrasonic flowmeter, mass flow Metering and open channel flow meter. The advantages and disadvantages of various flowmeters and the main application areas are shown in Table 1. (Because there are many kinds of mass flowmeters, the advantages and disadvantages of each other and the application range are different, so they are not listed in the table): (The similar quasi-numbers for the characterization of viscous effects in fluid dynamics are denoted as Re.Re = ÏvL/μ. Ï, μ are fluid densities and viscosities, and v, L are the characteristic velocity and characteristic length of the flow field. The Reynolds number is small, meaning fluid flow. The viscous force of each particle dominates the flow, and the fluid particles flow in a regular manner parallel to the inner wall of the pipeline, showing a laminar flow state. The Reynolds number is large, which means that the inertial force dominates, and the fluid is in a turbulent flow state.) 2 electromagnetic flow meter measurement principle According to Faraday’s Law of Electromagnetic Induction, when a conductor moves magnetic field lines in a magnetic field, induced electromotive force e will be generated at both ends of the conductor. Its direction is determined by the right-hand rule, its magnitude and the magnetic field strength B, and the conductor is in the magnetic field. The effective length L is proportional to the moving speed u of the conductor perpendicular to the magnetic field. If B, L, u are mutually perpendicular, then: e = BLu Similarly, if a magnetically non-magnetically permeable pipe with an inner diameter D is placed perpendicular to the direction of the magnetic field in a uniform magnetic field of magnetic induction B, the conductive liquid cuts the magnetic lines when the conductive liquid moves in the pipe at a flow rate u. A pair of electrodes are installed on both sides of the pipe perpendicular to the diameter of the magnetic field (as shown in Figure 1). It can be proved that as long as the velocity distribution in the pipeline is symmetrical with the axis, an induced electromotive force will be generated between the two electrodes: e=kBDÅ« In the formula, Å« is the average flow velocity (m/s) on the pipe section; k is the constant coefficient, dimensionless; D is the diameter of the measuring tube (m); B is the magnetic induction intensity (T). This results in volumetric flow through the pipe: From the above equation, when the measuring tube structure is certain, the volume flow qv is proportional to the ratio e/B, but independent of the fluid state and the physical property parameters, the measurement ratio e/B can obtain the volume flow value qv. When the magnetic induction B is a constant value, the volume flow qv is proportional to the induced electromotive force e. B is the magnetic induction of a DC magnetic field or a sine wave AC magnetic field or other type of magnetic field. It is provided by the excitation system of the electromagnetic flowmeter. Excitation systems can provide electromagnetic flow sensors with multiple forms of magnetic field waveforms. Different magnetic field waveforms directly determine the characteristics of the electromagnetic field sensor's working magnetic field, and also basically determine the processing method of the electromagnetic flowmeter's flow signal, which has a great influence on the working performance of the electromagnetic flowmeter. 3 electromagnetic flowmeter field application data and analysis The on-site test of the flow rate of clay cement slurry measured by an electromagnetic flowmeter was carried out on the site of pre-grouting on the ground of a gangue well in the Jijixi Coal Mine, Jibei Coal and Power Group. The clean water and the three ratios of the clay cement slurry were tested during the test. The specific gravity of fresh water was 1.00 g/cm3, and the specific gravities of the three types of clay cement were 1.21 g/cm3, 1.33 g/cm3, and 1.39 g/cm3, respectively. Since the technology of the electromagnetic flowmeter for measuring the clear water flow is already very mature, the flow rate of the clear water measured by the electromagnetic flowmeter is used as the standard data in the test process, and the data when measuring the clay cement slurry is compared with it to determine the accuracy of its measurement. . The pump volume used for the injection pump during the test was 99L/min; during the test, the injection line was open without pressure; the test time was 65 minutes, and the sampling interval was 5 minutes. The specific test data is shown in Table 2. The comparison curves of the four groups of data are shown in Figure 2. According to the test data, the average instantaneous flow rate of clear water was 1.327m/s. The average instantaneous flow velocity of clay cement with a specific gravity of 1.21g/cm3 was 1.31m/s; the average instantaneous flow velocity of clay cement with a specific gravity of 1.33g/cm3 was 1.324m. /s; The average instantaneous flow velocity of clay cement with a specific gravity of 1.39 g/cm3 is 1.323 m/s, and the average instantaneous flow velocity of clear water is between -0.232% and -1.304%. 4 Conclusion After field test, within the scope of the test, the error between the flow rate of the cement slurry measured by the electromagnetic flowmeter and the flow rate of the clear water is not more than 1.4%, which is in accordance with the practical application requirements of the field engineering. The current manual measurement can be replaced when the pump volume is 99L/table 2 electromagnetic flowmeter to measure water and cement slurry data comparison table min. If you need to further improve the accuracy of the measurement, you can recalibrate it before the measurement, or increase the loss factor by about 1% during the measurement. Due to the great difference between the measurement in the construction and the laboratory measurement, the measurement accuracy of the electromagnetic flowmeter in the field test has been able to meet the needs of the construction. In order to ensure the accuracy of measurement, the construction site should pay attention to ensure that the pipeline is full, and try to keep the measuring instrument away from the strong electromagnetic environment and to avoid severe vibration of the instrument. Textiles Baling Machine,Textile Balers,Textile Baler Machine,Hydraulic Baling Press DILOYA GROUP CO.,LTD. , https://www.diloyarecycle.com
1 types and advantages and disadvantages of flow measurement instruments 
