Selection and installation of electromagnetic flow meter

Abstract: The selection and installation of electromagnetic flow meters are provided by excellent flowmeter and flowmeter manufacturers. 1. First of all, the measurement requirements of this unit should be specified. There are several measurement requirements, mainly including: measurement medium, flow m3/h (minimum, working point, maximum), medium temperature ℃, medium pressure MPa, installation form (pipeline or plug-in) etc. two,. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the details of the selection and installation of electromagnetic flowmeters. 1. First of all, the measurement requirements of this unit should be specified. There are several measurement requirements, mainly including: measurement medium, flow m3/h (minimum, working point, maximum), medium temperature ℃, medium pressure MPa, installation form (pipeline or plug-in) etc. 2. Prerequisites for the selection of electromagnetic flowmeters 1. The measured medium must be a conductive liquid (that is, the measured fluid is required to have a minimum electrical conductivity). 2. The measured medium should not contain a lot of ferromagnetic medium or a lot of bubbles. 3. The measurement principle of electromagnetic flowmeter should be understood. The measurement principle is based on Faraday's law of electromagnetic induction, that is, when the flow is measured, the fluid flows through a magnetic field perpendicular to the flow direction, and the flow of the conductive fluid induces a flow rate that is related to the average flow rate (also known as volume flow rate). ) is proportional to the voltage, the voltage signal is detected by two electrodes in direct contact with the fluid, and transmitted through the cable to the amplifier, which is then converted into an output signal. Fourth, the main characteristics of electromagnetic flowmeter should be understood. The main characteristics are: (1) There is basically no pressure loss in the measuring tube, it is not easy to be blocked, and it has unique adaptability to the measurement of slurry; (2) The straight pipe section has low requirements; (3) The low-frequency rectangular wave excitation is not subject to The influence of power frequency and on-site distribution interference, the work is stable and reliable; (4) The body of the transmitter can be made of all stainless steel, and it has anti-acid, anti-alkali and anti-corrosion capabilities after adding lining materials; (5) The field display converter can use special intelligent Chip, parameter setting is convenient; ⑹ The transmitter can be equipped with a self-calibration system, which can self-calibrate the transmitter constants and factory calibration values ​​at any time, which is convenient for debugging and maintenance; ⑺ The measurement range is wide, and the full-scale flow rate can be set at 0.3m/s—12m/s range; ⑻ its plug-in type can be installed or dismantled in the state of continuous flow; ⑼ wide range of use: can be used in chemical, metallurgy, paper, food, petroleum, urban water supply and other fields. Five, the selection points of the model 1, the first and foremost is to choose the pipeline type geomagnetic flowmeter, or the insertion type electromagnetic flowmeter. 2. Under normal circumstances, the electromagnetic flowmeter without display on site is selected, and its output 4—20mA (or 0—10 mA) current signal to the secondary instrument in the control room and can display the flow and total amount. 3. If it is emphasized that it is convenient to observe the flow in the pipeline during on-site operation, the on-site display electromagnetic flowmeter can be selected. 4. When the environmental requirements or measurement accuracy requirements are high, the safe voltage intelligent electromagnetic flowmeter can be selected. 5. When measuring flow with a large pipe diameter above 200mm or installing and disassembling in a state of continuous flow, the plug-in or enhanced plug-in electromagnetic flowmeter can be preferred. Six, the selection points of the sensor diameter 1. The diameter of the sensor is selected to be the same as the diameter of the connected process pipe. The advantage is that it is easy to install (no need for a reducer); the premise is that the flow rate of the fluid in the pipe must be within 0.3m/s—Within the range of 10m/s; its applicable state is that it is used in the early stage of the project and the fluid velocity in the pipe is in a low state. 2. Select the diameter of the sensor and the diameter of the connected process pipeline. Its applicable state: (1) the flow rate is low and the flow rate is stable; (2) the cost performance is reduced. 7. The selection points of lining materials are selected by the orderer according to the corrosiveness, wearability and temperature of the measured medium of the company, and can refer to the information provided by each manufacturer.“Lining material properties and scope of application”. 8. The selection of electrode materials is selected by the orderer according to the corrosiveness of the medium to be tested by the company. Please refer to the information provided by each manufacturer.“Electrode material corrosion resistance table”. 9. Selection of protection level According to the national standard GB4208-84, the protection level of the shell is as follows: if the instrument is installed below the ground and is often flooded, the submersible type should be selected; if the instrument is installed on the surface, the water-proof type should be selected. 10. Selection of upper limit flow 1. Generally, the diameter of the transmitter is selected to be the same as the diameter of the connected piping. Since there is a strict functional relationship between the diameter, the flow rate and the flow rate, you can refer to the upper limit flow table of the electromagnetic flowmeter provided by the manufacturer when choosing, and select the upper limit flow value under the corresponding diameter. 2. When the flow rate in the process piping is low, it cannot be reached“1”When the minimum upper limit flow value under the corresponding diameter is selected, the diameter of the transmitter can be selected to be smaller than the diameter of the process piping, that is, reducers are added before and after the transmitter. 11. Selection of installation form 1. Integral type: The sensor part and the conversion part of the flowmeter are integrated into one, and the advantage is that it is easy to install. 2. Separate type: The sensing part of the flowmeter is installed on the pipeline under test, and the conversion part is installed in a room that is easy to operate. It is suitable for occasions with poor on-site environment (but the separation length should be less than 30m). 12. Selection of grounding ring If the pipeline connected to the instrument is insulating relative to the measured medium, a grounding ring should be selected. 13. Prerequisites for the selection of ball valves For the occasions where the process requires that the fluid flow in the pipeline must not be stopped and the medium must not overflow, it is necessary to install a ball valve. As for the flowmeter that is allowed to be cut off when assembling and disassembling the flowmeter (or the assembly and disassembly operation does not affect the pipeline work), it is not necessary to install the ball valve and the flowmeter is directly installed on the flange short pipe.
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