Electromagnetic FlowmeterThe structure mainly consists of a magnetic circuit system, a measuring conduit, electrodes, a housing, a lining, and a converter.

Magnetic Circuit System:Its function is to generate a uniform DC or AC magnetic field. The DC magnetic circuit is implemented using a magnet, which has the advantages of a relatively simple structure and less interference from AC magnetic fields. However, it can easily polarize the electrolyte liquid inside the measuring tube, causing the positive electrode to be surrounded by negative ions and the negative electrode to be surrounded by positive ions, resulting in electrode polarization and an increase in internal resistance between the two electrodes, which seriously affects the normal operation of the instrument. When the diameter of the pipeline is large, the corresponding magnet is also large, bulky, and uneconomical. Therefore, electromagnetic flow meters generally use alternating magnetic fields and are excited by 50HZ power supply.

Measurement catheter:Its function is to allow the tested conductive liquid to pass through. In order to divert or short-circuit the magnetic flux when the magnetic field lines pass through the measuring conduit, the measuring conduit must be made of non-magnetic, low conductivity, low thermal conductivity, and materials with certain mechanical strength, such as non-magnetic stainless steel, fiberglass, high-strength plastic, aluminum, etc.

Electrode:Its function is to generate an induced potential signal proportional to the measured value. The electrode is generally made of non-magnetic stainless steel and is required to be flush with the lining so that fluid can pass through without obstruction. Its installation position should be in the vertical direction of the pipeline to prevent sediment from accumulating on it and affecting measurement accuracy.

Shell:Made of ferromagnetic materials, it is the outer cover of the distribution system excitation coil and isolates the interference of external magnetic fields.

Lining:There is a complete layer of electrical insulation lining on the inner side of the measuring conduit and the flange sealing surface. It directly contacts the liquid being measured, and its function is to increase the corrosion resistance of the measuring conduit and prevent the induced potential from being short circuited by the metal measuring conduit wall. The lining materials are mostly corrosion-resistant, high-temperature resistant, wear-resistant polytetrafluoroethylene plastics, ceramics, etc.

converter:The induced potential signal generated by liquid flow is very weak and greatly affected by various interference factors. The function of the converter is to amplify and convert the induced potential signal into a unified standard signal and suppress the main interference signal. Its task is to amplify and convert the induced potential signal Ex detected by the electrode into a unified standard DC signal.

Electromagnetic Flowmeterfeature

1. Measurement is not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;

2. Measure the flow components inside the tube, with no pressure loss and low requirements for straight pipe sections. Adaptability to slurry measurement;

3. Reasonably selecting sensor lining and electrode materials, which have good corrosion resistance and wear resistance;

4. The converter adopts a novel excitation method, with low power consumption, zero point stability, and high degree. The flow range can reach 150:1;

5. The converter can be integrated or separated from the sensor;

6. The converter adopts a 16 bit high-performance microprocessor, 2x16 LCD display, convenient parameter setting, and reliable programming;

7. The flowmeter is a bidirectional measurement system equipped with three integrators: forward total, reverse total, and differential total; It can display positive and negative flow rates and has multiple outputs: current, pulse, digital communication HART；

8. The converter adopts surface mount technology (SMT) and has self checking and self diagnostic functions;

9. The measurement accuracy is not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity. The sensor's induced voltage signal is linearly related to the average flow rate, resulting in high measurement accuracy.

10. There is no obstruction in the measuring pipeline, so there is no additional pressure loss; There are no movable parts inside the measuring pipeline, so the sensor has an extremely long lifespan.

11. Due to the fact that the induced voltage signal is formed in the entire space filled with a magnetic field and is the average value on the surface of the pipeline, the sensor requires a shorter straight pipe section, with a length of 5 times the diameter of the pipeline.

12. The converter adopts Z high-tech microcontroller (MCU) and surface mount technology (SMT), with reliable performance, high accuracy, low power consumption, stable zero point, and convenient parameter setting. Click on the Chinese display LCD to show cumulative flow, instantaneous flow, flow rate, flow percentage, etc.

13. A bidirectional measurement system that can measure both forward and reverse flow rates. Using special production processes and materials to ensure the stability of product performance over a long period of time.

Electromagnetic Flowmeterclassification

According to the different types of external magnetic fields, there are mainly two types of electromagnetic flow meters: DC type and induction type. External constant lower magnetic field of DC electromagnetic current drought meter (Figure 2)BPerpendicular to the axis of the pipe,CTheDTwo electrodes are installed at the location to measure the electromotive force induced by the fluid crossing the magnetic fieldU. TrafficQThe following equation can be used to calculate:

in the formulaAThe cross-sectional area of the pipeline;dFor the diameter of the pipeline;kTo adjust the coefficient, it is used to correct the influence of factors that were not taken into account when exporting the formula, such as the fact that the flow velocity inside the flowmeter pipeline is not uniform. In conventional flow meters,kApproximately 0.8, but for electromagnetic flow meters of specific sizes and used for specific operating conditions, the volumetric method (the volume that flows over a certain period of time) needs to be used for calibrationkValue. The magnetic field can be generated by a magnet, which is usually made of aluminum nickel cobalt alloy. When the flow rate is high, due to the large diameter of the pipe, a coreless excitation winding is used to generate an approximately uniform magnetic field by passing a constant DC current through it.

Induction electromagnetic flowmeter can be used in situations where the measured fluid temperature is too high or has a strong corrosive effect on the electrode (Figure 2). A. B is two AC excitation windings with equal turns (shown in cross-section in the figure), which are connected in series but have opposite current directions. When the fluid is stationary, the synthesized magnetic flux through the induction coil C is zero, so there is no induced alternating electromotive force in the coil. When fluid flows, an alternating electromotive force is generated in the induction coil, and its magnitude is proportional to the flow velocity. Based on this principle, there are many modification plans. For example, using an excitation winding with opposite direction induction coils placed on each side of its symmetry and connected in series (Figure 3), when the fluid flows, the magnetic field lines move in the direction of the flow, causing the large electromotive force in the induction coils on both sides to be non-zero, indirectly indicating the magnitude of the flow rate.

Electromagnetic FlowmeterThere are no other components inside the pipeline, so in addition to measuring the flow rate of conductive fluids, it can also be used to measure the flow rate of non-conductive liquids of various viscosities (containing ionizable substances). Electromagnetic flow meters are often used in the nuclear energy industry.

Figure 2 DC electromagnetic flowmeter

Figure 3 Induction electromagnetic flowmeter

Electromagnetic FlowmeterThe display methods are divided into: split type electromagnetic flowmeter and integrated type electromagnetic flowmeter. Series nominal diameter DN15~DN3000.

Split typeElectromagnetic FlowmeterIt is an induction instrument that measures the volume flow rate of conductive medium inside a tube based on Faraday's law of electromagnetic induction. It uses embedded microcontroller technology to achieve digital excitation, and adopts CAN fieldbus on the electromagnetic flowmeter. It belongs to the domestic * and has reached the high-tech level in China.

The split type electromagnetic flowmeter can not only meet on-site display requirements, but also output 4-20mA current signals for recording, regulation, and control. It has been widely used in industrial technology and management departments such as chemical, environmental protection, metallurgy, medicine, papermaking, and water supply and drainage.

Split typeElectromagnetic FlowmeterIn addition to measuring the flow rate of general conductive liquids, it can also measure the volumetric flow rate of liquid-solid two-phase flow, high viscosity liquid flow, and salt, strong acid, and strong alkali liquids.

The integrated electromagnetic flowmeter is developed based on Faraday's law of electromagnetic induction and is used to measure the volumetric flow rate of conductive fluids. Due to the characteristics of *, it has been widely used in the measurement of various conductive liquids in industry. Mainly used in industries such as chemical, papermaking, food, textile, metallurgy, environmental protection, and water supply and drainage, it can achieve system control when paired with computers.

1．Electromagnetic FlowmeterThere are no movable parts or flow barriers, which will not cause pressure loss, wear, blockage, or other issues.

2. Electromagnetic flowmeter is a volumetric flow measurement instrument that is not affected by the temperature, viscosity, density, and conductivity (within a certain range) of the measured medium during the measurement process.

3. The range of electromagnetic flowmeter is wide, up to 1:100. In addition, electromagnetic flow meters are only proportional to the average flow velocity of the measured medium, and are independent of axisymmetric flow states (laminar or turbulent).

4. Electromagnetic flowmeter has no mechanical inertia, sensitive response, can measure instantaneous pulsating flow rate, and has good linearity. Therefore, the measurement signal can be directly converted into a standard signal output linearly using a converter. LD-T type can indicate on-site, while LD type can transmit over long distances.

select

Selection of Caliber and Range

The diameter of the transmitter is usually chosen to be the same as that of the pipeline system. If the distribution system needs to be designed, the diameter can be selected based on the range and flow rate of the manifold. For electromagnetic flow meters, a flow rate of 2-4m/s is more suitable. In special circumstances If there are solid particles in the liquid, considering the wear situation, a commonly used flow velocity of ≤ 3m/s can be selected. For fluids that are easily attached to the pipe wall, a flow velocity of ≤ 2m/s can be selected. After the flow velocity is determined, it can be adjusted according to

To determine the diameter of the transmitter.

The range of the transmitter can be selected based on two principles: first, if the instrument's full range is greater than the expected Z-flow Z-value, and second, if the normal flow address is greater than 50% of the instrument's full range to ensure a certain measurement accuracy.

Lining selection

Correct selection method of lining material for electromagnetic flowmeter

The lining material should be selected based on the corrosiveness, wear resistance, and temperature of the tested medium:

1、 Natural rubber (soft rubber)

1. Good elasticity, wear resistance, and tensile strength

2. Resistant to corrosion from general weak acids and bases

3. Water and sewage measurement

2、 Acid resistant rubber (hard rubber)

Can withstand corrosion from hydrochloric acid, acetic acid, oxalic acid, ammonia water, phosphoric acid at room temperature, as well as 50% sulfuric acid, sodium hydroxide, and potassium hydroxide, but is not resistant to corrosion from strong oxidants

Measure general acid, alkali, and salt solutions

3、 Neoprene rubber

1. Good elasticity, high tensile strength, and wear resistance

2. Resistant to corrosion from low concentration acid-base and salt solutions, but not resistant to corrosion from oxidizing media

<80℃；

Measure water, sewage, mud and slurry

4、 Polyurethane rubber

1. Wear resistance of *

2. Poor acid and alkaline resistance

<40℃

Coal slurry, mud, and slurry for measuring neutral and strong wear

5、 Polytetrafluoroethylene (PTFE)

1. Boiling resistant hydrochloric acid, sulfuric acid, nitric acid, aqua regia, concentrated alkali, and various organic solvents

2. Good wear resistance, poor adhesion performance

-80～+180℃；

Measurement of concentration, strong corrosive solutions with concentrated alkali, and sanitary media

Application site selection

1. Understand the process parameters

(1) Understand the name of the tested liquid (provided by the user)

(2) Understand the Z-high flow rate, common flow rate, and Z-low flow rate of the tested liquid (provided by the user)

(3) Understand the process pipe diameter (provided by the user)

(4) Understand the temperature of the medium (provided by the user)

(5) Understand the pressure of the medium (provided by the user)

(6) Understand the conductivity of the tested fluid (provided by the user)

(7) Understand whether there is negative pressure (provided by the user)

2. Preliminary selection

(1) Determine whether to use an electromagnetic flowmeter based on the name and properties of the measured medium (to be determined by the salesperson)

Attention: Electromagnetic flow meters can only measure the flow rate of conductive liquids, while gases, oils, and the vast majority of organic liquids are not included in the general category of conductive liquids

(2) Determine the electrode material based on the properties of the dielectric material learned

Attention The company generally provides four types of electrodes: stainless steel, Hastelloy, titanium, and tantalum. The selection of which electrode should be based on the properties of the medium and relevant information manuals

(2) Determine whether to use rubber or PTFE lining based on the temperature of the medium learned (to be determined by the marketer)

Attention: The temperature resistance of rubber should not exceed 80C;

PTFE can withstand a temperature of 150C and can instantly withstand 180C;

Urban sewage can generally be treated with rubber lining and stainless steel electrodes

(3) Based on the learned medium pressure, select the flange specification for the body (to be determined by the marketer)

Attention: The specification of electromagnetic flanges is usually that when the diameter ranges from DN10 to 250, the rated pressure of the flange is ≤ 1.6Mpa;

When the diameter ranges from DN250 to 1000, the rated pressure of the flange is ≤ 1.0Mpa;

When the actual pressure of the medium is higher than the corresponding range of pipe diameter pressure mentioned above, it is a special order, but the high pressure of Z shall not exceed 6.4Mpa

(4) Determine the conductivity of the medium

Attention: (1) The conductivity of the electromagnetic flowmeter shall not be lower than 5uS/cm

(2) The conductivity of tap water is about tens to hundreds of uS/cm. Generally, boiler soft water (deionized water) is conductive, while pure water (highly distilled water) is non-conductive

(3) The conductivity of gases, oils, and the vast majority of organic liquids is much lower than 5uS/cm, making them non-conductive.

3. Understand user requirements

(1) Understand whether it is a combination type on-site display or a split type remote transmission display (provided by the user)

Attention: When displaying as a separated remote transmission, please be aware of the Z-distance, which is 100 meters apart

(2) Understand if additional features are needed (provided by the user)

Attention: 1. The electromagnetic flowmeter itself has upper and lower limit flow alarm, frequency and current output functions, and does not require special ordering

2. The sealing protection level of the electromagnetic flowmeter housing is IP65 and IP68. When choosing the submersible IP68, it is a special order

3. When the electromagnetic flowmeter needs to be connected to a computer, an RS-485 communication port needs to be added, which is a special order

4. Selection: After the above steps, the model and specifications of the electromagnetic flowmeter can be determined.

Electromagnetic FlowmeterInstructions for use

The electromagnetic flowmeter has two operating states: automatic measurement state and parameter setting state.
When the instrument is powered on, it automatically enters the measurement state. In automatic measurement mode, the electromagnetic flowmeter automatically completes various measurement functions and displays corresponding measurement data. In the parameter setting state, the user uses four panel keys to complete the instrument parameter setting.
1. Key function

1.1 Key functions in automatic measurement mode
Down key: Loop through the selection screen to display content in the downward direction;
Up key: Loop through the screen to select the up display content;
Composite key+confirm key: enter parameter setting state;
Confirm button: Return to automatic measurement mode;
Adjustment of LCD display contrast in measurement state: The small LCD is adjusted by pressing the "composite key+up key" or "composite key+down key" for a few seconds; The large LCD is achieved by adjusting the potentiometer on the back of the large LCD.
1.2 Key functions in parameter setting state
Down key: Subtract 1 from the number at the cursor;
Up key: add 1 to the number at the cursor;
Composite key+down key: Move the cursor to the left;
Composite key+up key: Move the cursor to the right;
Confirm key: Enter/Exit submenu;
Confirm button: Press continuously for two seconds in any state to return to automatic measurement mode.
Note: When using the "composite key", you should first press the composite key and then simultaneously hold down the "up key" or "down key"
2. In the parameter setting state, if there is no button operation within 3 minutes, the instrument will automatically return to the measurement state.
3. The flow direction selection for zero point correction of flow can be switched by moving the cursor to the "+" or "-" on the left side of Z and using the "up" or "down" keys to make it opposite to the actual flow direction.
4. To select the unit of flow, you can move the cursor to the original displayed flow unit in the "Flow Range Setting" menu, and then use the "Up" or "Down" keys to switch to meet your needs.
2. Parameter setting function key operation
To set or modify the parameters of an electromagnetic flowmeter, it is necessary to transition the flowmeter from the measurement state to the parameter setting state. In the measurement state, press the "composite key+confirm key" to display the state transition password (0000). According to the confidentiality level, modify the password provided by the manufacturer accordingly. After pressing the "composite key+confirm key" again, it will enter the desired parameter setting state.

Installation of Intelligent Electromagnetic Flow Meter Sensor on Process Pipeline

1. The intelligent electromagnetic flowmeter blockage tube must be filled with medium at any time and cannot work normally without filling or emptying the tube. When the medium is not fully filled in the pipe, the method of raising the height of the outlet pipe at the back of the flowmeter can be used to fill the pipe with the medium, avoiding the incomplete pipe and gas from adhering to the electrode.

2. Vacuum inside the pipeline can damage the lining of the flowmeter, so special attention should be paid.
3. The positive direction of flow should be consistent with the positive direction indicated by the arrow on the flowmeter.
4. The intelligent electromagnetic flowmeter can be installed on straight pipelines, as well as on horizontal or inclined pipelines, but it requires that the center line of the two electrodes be in a horizontal state.
5. For liquid and solid two-phase fluids, vertical installation is used to allow the measured medium to flow from top to bottom, which can evenly wear the lining of the flowmeter and extend its service life.
6. Ensure that there is sufficient space near the pipeline flange for the installation and maintenance of the flowmeter.
If there is vibration in the measuring pipeline, there should be fixed supports on both sides of the flowmeter.
8. If the measuring medium is a heavily polluted liquid, a flowmeter body can be installed in the bypass pipeline without interrupting the process operation, which can be emptied and cleared.

9. When installing a flow meter with PTFE lining, the bolts connecting the flange should be tightened evenly, otherwise it is easy to crush the PTFE lining. Use a torque wrench.

Extended reading: Mingyu self-control flowmeter