已经被人们广泛应用，并得到人们的认可，现举例说明。 Plug-in electromagnetic flowmeters have been widely used and recognized by people. In order to reduce pollution and save water and emissions, strict measurement and control of domestic water, industrial water, circulating water, and discharged sewage must be performed. Flow measurement occupies an important position in the implementation of total water resources control, quota management, and petrochemical production and process control. The main water supply plant for circulating water in the coal chemical plant area. The normal operation of the water supply device of the plant is vital to the production and environmental protection of the whole plant. Sewage treatment capacity and treatment quality are important indicators of the water supply device. If the treatment capacity is low, it cannot meet the water requirements of the entire plant, and if the treatment quality is low, it cannot meet the discharge requirements. When examining the water discharge capacity and economic benefits of mine water, three flow indicators are mainly considered, namely the inflow of mine water, the outflow of clarified water and the outflow of sludge. In consideration of cost-effectiveness and other factors, a Shanghai company reported that it used a plug-in electromagnetic flowmeter on a pipe of Φ250mm or more and installed it under pressure. After nearly 5 months of operation test, the flowmeter has a good application effect and the flowmeter is accurate .
1. Technical analysis
工作原理是基于法拉第电磁感应定律，测量流量时，液体流过垂直于流动方向的磁场，感应出一个与平均流速(体积流量)成正比的电压。 1.1 Working principle The working principle of the plug-in electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When measuring the flow, the liquid flows through a magnetic field perpendicular to the flow direction, and a voltage proportional to the average flow rate (volume flow) is induced. The induced voltage signal is detected by two electrodes that are in direct contact with the liquid, and transmitted to the smart transmitter through a dedicated cable. The smart transmitter performs calculations based on the magnitude of the potential and the mathematical model of the electromagnetic flow, and converts it into a flow signal (including instantaneous Quantity and cumulative quantity) for on-site display, and then output the standard 4-20 MA and 1 ～ 5VDC signals to the flow secondary meter or DCS. 1.2 Composition The plug-in electromagnetic flowmeter is mainly composed of a sensor, a smart transmitter and a dedicated cable. (1) The sensor is composed of an electrode and an excitation line 罔, and its function is to generate a corresponding induced potential (5-60 mV) on the electrode according to the speed of the conductive medium (fluid) flowing through the excitation coil. (2) The function of the smart transmitter is to amplify the induced potential signal of the sensor, and then calculate it according to the mathematical model and formula of the potential flow, to obtain the flow result and the standard flow signal. The adjustment of various flow parameters and the setting of calibration parameters are performed on the smart transmitter. (3) The function of the special communication cable is that the sensor transmits the millivolt potential signal to the smart transmitter, and the smart transmitter provides the oscillation voltage to the excitation coil. Since the potential signal is a weak signal of 5-60 mV and the excitation signal is a high-frequency and low-amplitude oscillating signal, the cable must fully consider shielding and anti-interference. The length of the cable is directly proportional to the cross-sectional area and proportional to the electrical conductivity of the medium. The stronger the conductive characteristics, the longer the transmission distance. Generally, the transmission distance is 20 to 500 m. II Installation requirements 1.3.1 Ensure that when the fluid in the straight pipe section changes in direction, pipe diameter and valve opening, eddy current and flow field distortion will be generated, which will affect the measurement of the sensor electrodes and affect the accuracy of the instrument. Therefore, it is necessary to leave the pipe, hand valve, regulating valve and other components as far as possible. The specific requirements of the straight pipe section are shown in Table 1. In the table, D indicates the pipe diameter, and L indicates the distance from the sensor to parts such as valves or elbows. 1.3.2 Ensure the perpendicularity of the fluid and the magnetic field of the sensor. When installing pressure take-up stubs in pipe openings, pay attention to the vertical direction of the pressure take-up stubs. The angle between the short tube axis and the pipe axis after welding is 90. And, the extension line connected by the flange short pipe passes through the circle center of the pipe cross section vertically, so that the fluid can be perpendicular to the magnetic field. Third, try to avoid interference sources, in order to ensure measurement accuracy, the sensor should be avoided in places prone to vacuum, gas, eddy current and other places. The communication cable between the sensor and the smart transmitter should avoid strong electrical equipment such as motors.
在大口径管道中广泛使用，安装方便，价格低廉，很受各厂家的青睐，插入式电磁流量计除了有这些优点还有在线维护不用停产更大的优点，可以在安装座上加装一只隔离球阀，在系统不停运的情况下，实现在线插拔，保证系统的连续稳定运行。 Plug-in electromagnetic flowmeters are widely used in large-diameter pipelines, and are easy to install and inexpensive. They are very popular with manufacturers. In addition to these advantages, plug-in electromagnetic flowmeters have the advantages of online maintenance without stopping production. An isolation ball valve is added to the system to realize online plugging and uninterrupted operation to ensure continuous and stable operation of the system. The measuring principle of the plug-in electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. The measuring tube of the flowmeter is a non-magnetic alloy short tube lined with insulating material. The two electrodes pass through the pipe wall and are fixed on the measuring pipe along the pipe diameter direction. Its electrode tip is substantially flush with the inner surface of the liner. When the excitation coil is excited by a double-wave pulse, a working magnetic field with a magnetic flux density B in a direction perpendicular to the axis of the measuring tube will be generated. At this time, if a fluid with a certain conductivity flows through the measuring tube. Electromotive force E is induced by the cutting magnetic field lines. The electromotive force E is proportional to the magnetic flux density B, and the product of the inner diameter d of the tube and the average velocity v is measured. The electromotive force E (flow signal) is detected by the electrodes and sent to the converter through a cable. After the converter amplifies the flow signal, it can display the fluid flow, and can output pulses, analog current and other signals for flow control and adjustment. Although the plug-in electromagnetic flowmeter is simple to operate and requires less maintenance, long-term use will still cause the electrodes to become dirty or worn. Therefore, in order to ensure the accuracy of the measurement, it is necessary to perform regular maintenance on the plug-in electromagnetic flowmeter. For the plug-in electromagnetic flowmeter, the system must be shut down and the liquid in the pipeline must be emptied for disassembly before each maintenance. If a failure occurs during abnormal maintenance, the disassembly of the plug-in electromagnetic flowmeter has a great impact on continuous production efficiency. Therefore, an isolation ball valve can be installed on the mounting seat, and the system can be plugged and unplugged without stopping the system to ensure continuous and stable operation of the system.