Selection and correct use of electromagnetic flowmeter
/div> & nbsp;& nbsp; 1、 Working principle of electromagnetic flowmeter
& nbsp;& nbsp; The measurement principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction (as shown in Figure 1). The measuring tube of the flowmeter is a short non-magnetic alloy tube lined with insulating material. Two electrodes are fixed on the measuring tube through the tube wall along the pipe diameter direction, and the electrode head is basically flush with the inner surface of the lining. When the excitation coil is excited by bidirectional square wave pulse, a working magnetic field with magnetic flux density B will be generated in the direction perpendicular to the axis of the measuring tube. At this time, if the fluid with a certain conductivity flows through the measuring tube, the cutting magnetic line of force will induce the electromotive force E. The electromotive force E is proportional to the magnetic flux density B. the product of the inner diameter D of the measuring tube and the average velocity V is measured. The electromotive force E (flow signal) is detected by the electrode and sent to the converter through the cable. After amplifying the flow signal, the converter can display instantaneous flow and total amount, and output pulse, analog current and other signals for flow control or regulation.
& nbsp;& nbsp; The EMF formula is
& nbsp;& nbsp; E = 4BQ/（ π D）
& nbsp;& nbsp; Where: e - induced electromotive force; B - magnetic induction intensity; Q -- flow rate; D -- nominal diameter of flowmeter.
& nbsp;& nbsp; 2、 Structure, classification and selection of electromagnetic flowmeter
& nbsp;& nbsp; Electromagnetic flowmeter is composed of electromagnetic sensor and electromagnetic flow converter.
& nbsp;& nbsp; According to the function of the converter, it can be divided into base type and slurry type. The basic type is suitable for the detection of general process, and the diameter of the sensor is DN 15 ~ DN 2400; The slurry type is suitable for the measurement of pulp, pulp and paste, and the diameter of the sensor is DN 15 ~ DN 600.
& nbsp;& nbsp; According to the composition of basic type and slurry type and sensor, it can be divided into one type flowmeter (converter and sensor are integrated) or separate type flowmeter (converter and sensor are installed separately). The nominal diameter of one-piece flowmeter is limited to DNl5 ~ dn400, while the separated flowmeter includes all diameters. The integrated flowmeter can be directly installed on the pipeline, and the separated flowmeter can be installed on a specific wall or instrument panel.
& nbsp;& nbsp; According to different installation sites, electromagnetic flowmeter can be divided into ordinary electromagnetic flowmeter and explosion-proof electromagnetic flowmeter.
& nbsp;& nbsp; The output, display, alarm, parameter programming, communication and computer interface form of flow and total amount of various types of electromagnetic flowmeter are basically the same. A typical network connection is shown in Figure 2. Network connection is to realize the communication between multiple electromagnetic flowmeter and computer through a communication bus. The electromagnetic flowmeter converts the measured flow signal into digital signal and sends it out. Using Modbus protocol, multiple instruments can be connected on the network.
& nbsp;& nbsp; 3、 Main performance and characteristics of electromagnetic flowmeter
& nbsp;& nbsp; 1. Simple and reliable structure, no movable parts, no blocking parts, no pressure loss and fluid blockage, low requirements for straight pipe section< BR> & nbsp;& nbsp; 2. No mechanical inertia, fast response, good stability, can be used in automatic detection and program control system< BR> & nbsp;& nbsp; 3. It can be used to measure corrosive fluids such as strong acid, strong alkali and salt solution. Compared with turbine and vortex flowmeter, it is not affected by fluid density, viscosity, temperature, pressure and conductivity< BR> & nbsp;& nbsp; 4. The flow range is wide (30:1), and some manufacturers' products can even reach 1500:1, and the initial measured flow rate is as low as about 0.2m/s< BR> & nbsp;& nbsp; 5. At present, the electromagnetic flowmeter mostly adopts intelligent design, which can display the medium flow direction and empty pipe signal, and has the function of removing small signal migration& nbsp;< BR> & nbsp;& nbsp; 6. Remote control can be achieved through telephone network& nbsp;< BR> < BR> & nbsp;& nbsp; 4、 Precautions in the use of electromagnetic flowmeter < br > & nbsp& nbsp;< BR> & nbsp;& nbsp; 1. Requirements for measuring medium:
& nbsp; （ 1) The fluid medium to be measured must be conductive< BR> & nbsp; （ 2) The measured fluid medium must be filled with pipeline< BR> & nbsp; （ 3) The measured flow medium must be uniform.
& nbsp;& nbsp; 2. Installation requirements:
& nbsp; （ 1) It should be ensured that there is at least 5D (inner diameter of pipe) straight pipe section upstream of the sensor. If there is a fully open gate valve or regulating valve upstream, the length of straight pipe section upstream of the flowmeter should be increased to 10d; The straight pipe section at the downstream side of the flowmeter should generally be larger than 3D< BR> & nbsp; （ 2) The magnetic field of instrument installation site shall be less than 400A / m< BR> & nbsp; （ 3) Covering facilities shall be added in the places easily exposed to the sun, and the damage to the instrument caused by corrosive liquid dripping shall be prevented< BR> & nbsp; （ 4) The most important thing in reliable measurement is the installation of the electrode. The requirements of different manufacturers are different. For example, the e-mag type produced by Kaifeng factory requires the electrode to be completely immersed in liquid, while the yyd type produced by Yiwu factory needs to be calculated according to the inner diameter of the pipe, the pipe wall and the length of the transition flange. The specific installation method can refer to the factory instructions.
& nbsp;& nbsp; 5、 Field use
& nbsp;& nbsp; In order to meet the needs of water supply in the new era, five e-mag electromagnetic flow meters produced by Kaifeng plant have been installed in the water supply network of our plant in recent years. According to the actual operation, compared with ordinary water meters, the flow meters have the following advantages:
& nbsp;& nbsp; oneThe accuracy is reliable and the data is stable, which avoids the dispute between the customer and the ordinary water meter measurement error and improves the production efficiency.
Table 1
Straight pipe section
12D before the table and 2D after the table
10d before the table and 5D after the table
5D before the table and 10d after the table
0d before table 15d after table
Instantaneous flow m3 / h
Type of water meter
LXS - 100 mm Ningbo meter
fifty-four point four eight
fifty-four point seven two
fifty-four point seven four
fifty-three point eight two
LXS - 100 mm Jindong dry
fifty-four point four eight
fifty-four point zero seven
fifty-five point three four
fifty-three point one eight
LXS - 100 mm Jindong wet
fifty-three point two two
fifty-two point eight nine
fifty-one point eight eight
forty-six point zero three
E-mag 150 mm electromagnetic flowmeter
fifty-four point four eight
fifty-four point seven two
fifty-four point seven four
fifty-four point nine eight
& nbsp;& nbsp; 2. The requirements of field installation are low. Ordinary water meters have strict requirements on the front and back straight pipe sections installed on the pipeline, but electromagnetic flowmeter does not. Table 1 shows the instantaneous flow of three kinds of ordinary water meters and electromagnetic flowmeter in different straight pipe sections of the same pipeline. It can be seen from the table that the requirements of electromagnetic flowmeter on straight pipe sections are low.
& nbsp;& nbsp; 3. The structure of electromagnetic flowmeter is simple and the requirement of water quality is low. Because the pH value of the water in the oil area is high (about 8.4-8.5)9), many impurities lead to the corrosion of many water meters after long-term use, blocking the filter screen, resulting in measurement error. However, there is no rotating parts in the electromagnetic flowmeter, and there is no inaccurate measurement due to mechanical wear or impurity blockage, which reduces the failure of the instrument, reduces the maintenance cost, and saves a lot of cost.
& nbsp;& nbsp; The measurement principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction (as shown in Figure 1). The measuring tube of the flowmeter is a short non-magnetic alloy tube lined with insulating material. Two electrodes are fixed on the measuring tube through the tube wall along the pipe diameter direction, and the electrode head is basically flush with the inner surface of the lining. When the excitation coil is excited by bidirectional square wave pulse, a working magnetic field with magnetic flux density B will be generated in the direction perpendicular to the axis of the measuring tube. At this time, if the fluid with a certain conductivity flows through the measuring tube, the cutting magnetic line of force will induce the electromotive force E. The electromotive force E is proportional to the magnetic flux density B. the product of the inner diameter D of the measuring tube and the average velocity V is measured. The electromotive force E (flow signal) is detected by the electrode and sent to the converter through the cable. After amplifying the flow signal, the converter can display instantaneous flow and total amount, and output pulse, analog current and other signals for flow control or regulation.
& nbsp;& nbsp; The EMF formula is
& nbsp;& nbsp; E = 4BQ/（ π D）
& nbsp;& nbsp; Where: e - induced electromotive force; B - magnetic induction intensity; Q -- flow rate; D -- nominal diameter of flowmeter.
& nbsp;& nbsp; 2、 Structure, classification and selection of electromagnetic flowmeter
& nbsp;& nbsp; Electromagnetic flowmeter is composed of electromagnetic sensor and electromagnetic flow converter.
& nbsp;& nbsp; According to the function of the converter, it can be divided into base type and slurry type. The basic type is suitable for the detection of general process, and the diameter of the sensor is DN 15 ~ DN 2400; The slurry type is suitable for the measurement of pulp, pulp and paste, and the diameter of the sensor is DN 15 ~ DN 600.
& nbsp;& nbsp; According to the composition of basic type and slurry type and sensor, it can be divided into one type flowmeter (converter and sensor are integrated) or separate type flowmeter (converter and sensor are installed separately). The nominal diameter of one-piece flowmeter is limited to DNl5 ~ dn400, while the separated flowmeter includes all diameters. The integrated flowmeter can be directly installed on the pipeline, and the separated flowmeter can be installed on a specific wall or instrument panel.
& nbsp;& nbsp; According to different installation sites, electromagnetic flowmeter can be divided into ordinary electromagnetic flowmeter and explosion-proof electromagnetic flowmeter.
& nbsp;& nbsp; The output, display, alarm, parameter programming, communication and computer interface form of flow and total amount of various types of electromagnetic flowmeter are basically the same. A typical network connection is shown in Figure 2. Network connection is to realize the communication between multiple electromagnetic flowmeter and computer through a communication bus. The electromagnetic flowmeter converts the measured flow signal into digital signal and sends it out. Using Modbus protocol, multiple instruments can be connected on the network.
& nbsp;& nbsp; 3、 Main performance and characteristics of electromagnetic flowmeter
& nbsp;& nbsp; 1. Simple and reliable structure, no movable parts, no blocking parts, no pressure loss and fluid blockage, low requirements for straight pipe section< BR> & nbsp;& nbsp; 2. No mechanical inertia, fast response, good stability, can be used in automatic detection and program control system< BR> & nbsp;& nbsp; 3. It can be used to measure corrosive fluids such as strong acid, strong alkali and salt solution. Compared with turbine and vortex flowmeter, it is not affected by fluid density, viscosity, temperature, pressure and conductivity< BR> & nbsp;& nbsp; 4. The flow range is wide (30:1), and some manufacturers' products can even reach 1500:1, and the initial measured flow rate is as low as about 0.2m/s< BR> & nbsp;& nbsp; 5. At present, the electromagnetic flowmeter mostly adopts intelligent design, which can display the medium flow direction and empty pipe signal, and has the function of removing small signal migration& nbsp;< BR> & nbsp;& nbsp; 6. Remote control can be achieved through telephone network& nbsp;< BR> < BR> & nbsp;& nbsp; 4、 Precautions in the use of electromagnetic flowmeter < br > & nbsp& nbsp;< BR> & nbsp;& nbsp; 1. Requirements for measuring medium:
& nbsp; （ 1) The fluid medium to be measured must be conductive< BR> & nbsp; （ 2) The measured fluid medium must be filled with pipeline< BR> & nbsp; （ 3) The measured flow medium must be uniform.
& nbsp;& nbsp; 2. Installation requirements:
& nbsp; （ 1) It should be ensured that there is at least 5D (inner diameter of pipe) straight pipe section upstream of the sensor. If there is a fully open gate valve or regulating valve upstream, the length of straight pipe section upstream of the flowmeter should be increased to 10d; The straight pipe section at the downstream side of the flowmeter should generally be larger than 3D< BR> & nbsp; （ 2) The magnetic field of instrument installation site shall be less than 400A / m< BR> & nbsp; （ 3) Covering facilities shall be added in the places easily exposed to the sun, and the damage to the instrument caused by corrosive liquid dripping shall be prevented< BR> & nbsp; （ 4) The most important thing in reliable measurement is the installation of the electrode. The requirements of different manufacturers are different. For example, the e-mag type produced by Kaifeng factory requires the electrode to be completely immersed in liquid, while the yyd type produced by Yiwu factory needs to be calculated according to the inner diameter of the pipe, the pipe wall and the length of the transition flange. The specific installation method can refer to the factory instructions.
& nbsp;& nbsp; 5、 Field use
& nbsp;& nbsp; In order to meet the needs of water supply in the new era, five e-mag electromagnetic flow meters produced by Kaifeng plant have been installed in the water supply network of our plant in recent years. According to the actual operation, compared with ordinary water meters, the flow meters have the following advantages:
& nbsp;& nbsp; oneThe accuracy is reliable and the data is stable, which avoids the dispute between the customer and the ordinary water meter measurement error and improves the production efficiency.
Table 1
Straight pipe section
12D before the table and 2D after the table
10d before the table and 5D after the table
5D before the table and 10d after the table
0d before table 15d after table
Instantaneous flow m3 / h
Type of water meter
LXS - 100 mm Ningbo meter
fifty-four point four eight
fifty-four point seven two
fifty-four point seven four
fifty-three point eight two
LXS - 100 mm Jindong dry
fifty-four point four eight
fifty-four point zero seven
fifty-five point three four
fifty-three point one eight
LXS - 100 mm Jindong wet
fifty-three point two two
fifty-two point eight nine
fifty-one point eight eight
forty-six point zero three
E-mag 150 mm electromagnetic flowmeter
fifty-four point four eight
fifty-four point seven two
fifty-four point seven four
fifty-four point nine eight
& nbsp;& nbsp; 2. The requirements of field installation are low. Ordinary water meters have strict requirements on the front and back straight pipe sections installed on the pipeline, but electromagnetic flowmeter does not. Table 1 shows the instantaneous flow of three kinds of ordinary water meters and electromagnetic flowmeter in different straight pipe sections of the same pipeline. It can be seen from the table that the requirements of electromagnetic flowmeter on straight pipe sections are low.
& nbsp;& nbsp; 3. The structure of electromagnetic flowmeter is simple and the requirement of water quality is low. Because the pH value of the water in the oil area is high (about 8.4-8.5)9), many impurities lead to the corrosion of many water meters after long-term use, blocking the filter screen, resulting in measurement error. However, there is no rotating parts in the electromagnetic flowmeter, and there is no inaccurate measurement due to mechanical wear or impurity blockage, which reduces the failure of the instrument, reduces the maintenance cost, and saves a lot of cost.
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