1 Introduction Electromagnetic flowmeter (EMF for short) is a measuring instrument for measuring the volumetric flow rate of conductive liquids using Faraday's law of electromagnetic induction. In the early 1950s, EMF achieved industrial application. In recent years, EMF production has accounted for 5% to 6.5% of the total number of industrial flow meters in the world. Especially since 2000, this value has been increasing year by year. Electromagnetic flowmeter as a kind of industrial flow measurement instrument, there are some tips and precautions in its installation and use, here I combine some of my personal experience and discussion, hoping to make a contribution to the correct installation and use of electromagnetic flowmeter. 2. The use of magnetic flowmeter advantages The measurement channel of the electromagnetic flowmeter is a smooth straight pipe with no obstructing flow detection part, and it is not easy to block because it is suitable for measuring liquid-solid two-phase fluids containing solid particles or fibers, such as pulp, coal water slurry, pulp, mud, and sewage; Of course, electromagnetic flowmeters also have drawbacks. For example, it cannot measure liquids with low electrical conductivity, such as petroleum products and organic solvents; it cannot measure gases, vapors, and liquids containing large bubbles; general-purpose EMF cannot be used because of limitations of lining materials and electrical insulating materials. Measure higher temperature liquids. 3. Installation and Usage Precautions 3.1 General Considerations for Use During Use The liquid should have the conductivity required for the measurement and require a substantially uniform distribution of conductivity. Therefore, the flow sensor should be installed so as to avoid places where conductivity is not easily generated. For example, liquid medicine is added near the upstream of the sensor. The liquid addition point is preferably located downstream of the sensor. When used, the sensor tube must be filled with fluid (except for non-full tube types). When liquids are mixed, their distribution should be generally uniform. The liquid should be at the same potential as ground and must be grounded. If the process piping is made of plastics and other insulating materials, the transport liquid generates friction and static electricity and other causes, resulting in a potential difference between the liquid and the ground. 3.2 Flow Sensor Installation 3.2.1 Installation site Normal electromagnetic flow sensor housing protection is extremely IP65 (dust and spray water level specified in GB 4208), all the following requirements for the installation site: 1) When measuring the mixed phase fluid, select the place that will not cause phase separation; when measuring the two-component liquid, avoid installing in the downstream where the mixing is not uniform; when measuring the chemical reaction pipeline, install it in the downstream of the reaction fully completed segment; 2 ) Avoid as much as possible negative pressure in the measuring tube; 3.2.2 straight pipe length requirements If the valve can be used, it should be installed at an angle of 45o with the electrode cut-off direction and the electrode shaft, so the additional error can be greatly reduced. 3.2.3 Installation position and flow direction 3.2.4 Bypass Pipes, Easy-to-Clean Connections, and Pre-Inlet Holes To facilitate inspection and adjustment of the zero point when the process piping continues to flow and the sensors stop flowing, bypass tubes should be installed. However, large diameter pipe systems are often difficult to manage because of investment and location space constraints. It is difficult to correct the measured value according to the degree of contamination of the electrode, or to determine a criterion for the degree of contamination that does not affect the measured value. In addition to the above, using a non-contact electrode or a meter with a blade cleaning device electrode to solve some problems, sometimes also need to remove the inner wall attachments, according to Figure 2, can be removed without removing the sensor in place. For pipes with a pipe diameter greater than 1.5-1.6m, a hole is placed in the pipe near the EMF so that the inner wall of the sensor pipe is cleaned when the pipe is stopped. 3.2.5 Installation of negative pressure piping Fluoroplastic lining sensors should be used with caution in negative pressure piping systems; positive pressure piping systems should be designed to prevent negative pressures, such as piping systems with liquid temperatures above room temperature, closing the upstream and downstream shut-off valves of the sensor and stopping the operation, the fluid cooling shrinks and forms a negative pressure. Pressure, should be installed near the sensor vacuum valve, as shown in Figure 3. According to the manufacturer's regulations, the absolute pressures of PTFE and PFA plastic linings used in negative pressure piping systems at 200C, 1000C, and 1300C must be greater than 27, 40, and 50 KPa, respectively. The sensor must be grounded separately (ground resistance 100Ω or less). In principle, the separation type should be grounded on the sensor side, and the converter grounding should be on the same grounding point. If the sensor is installed on the cathode corrosion protection pipeline, in addition to the sensor and the grounding ring together with the ground, but also use a thick copper wire (16mm2) to bypass the sensor across the two connecting flange flange, so that the cathodic protection current between the sensor isolation. Sometimes the stray current is too large. If the leakage current of the electrolytic cell along the electrolyte affects the normal measurement of the EMF, the electrical isolation between the flow sensor and its connected process can be taken. This method can also be used when the cathodic protection current affects EMF measurements on pipelines that are also cathodically protected. 3.3 Converter Installation and Connection Cables 4. in conclusion As the company moves toward the market, the company's production and operation management will be further deepened, and the flow measurement will become more and more important. As one of the industrial flow measuring instruments, the electromagnetic flow meter must play its role and how to properly install and use it on the basis of good selection. Has become a key issue. Therefore, under the premise of having certain professional knowledge, automated instrumentation professionals must master certain skills and methods in how to correctly install and use them. Only in this way can they meet the requirements of the company and make the flow metering play an important role. 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It does not produce the pressure loss caused by the detection of flow, the resistance of the instrument is only the resistance along the same length of the pipeline, energy saving effect is significant, the most suitable for large diameter water supply pipelines that require low resistance loss;
The volumetric flow rate measured by the electromagnetic flowmeter is virtually independent of the fluid density, viscosity, temperature, pressure, and electrical conductivity (as long as it is above a certain threshold).
Compared with most other flow meters, its front straight pipe section requires less;
Electromagnetic flowmeters have a large measuring range, typically 20:1 to 50:1, with a wide range of optional flow rates. The full-scale liquid flow rate can be selected within 0.5 to 10 m/s. Some models can be used to expand and reduce the flow in the field according to the need (for example, with a 4-digit potentiometer set the instrument constant) does not have to take off for offline flow calibration;
Electromagnetic flowmeter diameter than other types of flow meter wide, from a few millimeters to 3m; can measure positive and negative two-way flow, can also measure pulse flow, as long as the pulse frequency is much lower than the excitation frequency; instrument output is essentially linear;
The variety of materials that are easy to select with the fluid contact can be applied to corrosive fluids.
3) Choose a place with little vibration, especially for integrated type instruments;
4) Avoid large electric motors, large transformers, etc. nearby to avoid electromagnetic interference;
5) It is easy to realize the place where the sensor is grounded separately;
6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible;
7) The ambient temperature is in the range of -25/-10 to 50/600°C. The temperature of the integral structure is also controlled by the electronic components, and the range is narrower.
8) The relative humidity in the environment is in the range of 10% to 90%;
9) Avoid direct sunlight as much as possible;
10) Avoid rain soaking and will not be immersed in water.
If the degree of protection is IP67 (dust-proof and anti-submerged) or IP68 (dust-proof submersible), the above 8) and 10) requirements are not required.
In order to obtain normal measurement accuracy, the electromagnetic flow sensor must also have a straight pipe section of a certain length upstream, but its length is lower than that of most other flow meters. After the 90o elbow, T-tube, concentric reducer, and fully open valve, it is generally considered that as long as the distance from the electrode center line (not the sensor inlet end connection surface) is 5 times the diameter (5D) length of the straight pipe segment, valves with different opening degrees are required. 10D; The downstream straight section is (2~3)D or no requirement; but prevent the butterfly valve piece from protruding into the sensor measuring tube. The lengths of the upstream and downstream straight pipe sections proposed by various standards or verification regulations are also inconsistent. As summarized in Table 1, the requirements are higher than the usual requirements. This is due to the requirement to ensure that the current 0.5-level precision instrument is achieved. Table 1 
The sensor can be mounted horizontally, vertically or tilted without restriction. However, it is better to measure the solid and liquid two-phase fluids vertically and flow from bottom to top. This can avoid the disadvantages of local wear in the lower half of the liner during horizontal installation, solid phase sedimentation at low flow rates, and the like.
When installing horizontally, make the axis of the electrode parallel to the horizon, and do not be perpendicular to the horizon, because the electrode at the bottom is easy to be covered by the deposit, and the top electrode is easily wiped by the bubbles in the liquid to cover the surface of the electrode, causing the output signal to fluctuate. . In the piping system shown in Fig. 1, c and d are suitable positions; a, b, and e are unsuitable positions, and b may not be filled with liquid, and a and e are likely to accumulate gas, and the sensor may not be filled at a short position after the sensor at e. The drain is best shown as f-shaped. For the solid and liquid two-phase flow c is not an appropriate location. 
3.2.6 Grounding
The integral EMF does not have a separate converter; the discrete converter is installed near the sensor or in the instrument room, with a large selection of room, better environmental conditions than the sensor, and a degree of protection of IP65 or IP64 (dust and splash proof). The installation site requirements are the same as those in 3), 4), 6), 8), 9) and 10) in 3.2.1. The ambient temperature is limited by the electronic devices and the use temperature range is narrower than that listed in 7).
The distance between the converter and the sensor is limited by the conductivity of the measured medium and the signal cable type, ie, the distributed capacitance of the cable, the cross-section of the wire, and the number of shielding layers. Use the signal cable attached to the instrument (or model number) supplied by the manufacturer. Low conductivity liquids and longer transmission distances are also stipulated with three-layer shielded cables. The general instrument “operating instructions†gives the corresponding transmission distance range for different conductivity liquids. Single-layer shielded cables are usually used for industrial water or acid-base solutions and can travel over a distance of 100m.
In order to avoid interference signals, the signal cable must be put in the protective grounding pipe separately. The signal cable and the power cable cannot be installed in the same steel pipe.