Intelligent liquid electromagnetic flow is based on Faraday’s law of electromagnetic induction and is an inductive instrument for measuring the volumetric flow rate of conductive media. It consists of two parts: a sensor converter. In addition to measuring the volumetric flow rate of general conductive liquids, it can also be used to measure the volumetric flow rate of strongly corrosive liquids such as strong acids and alkalis, as well as homogeneous liquid-solid two-phase suspensions such as mud, slurry, and pulp. The product is widely used for flow measurement in industrial sectors such as petroleum, chemical, metallurgical, textile, papermaking, environmental protection, food, as well as in municipal management, water conservancy construction, river dredging and other fields.

Structure of liquid electromagnetic flowmeter

The structure of an electromagnetic flowmeter 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 permanent magnets, 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 permanent magnet is also large, bulky, and uneconomical. Therefore, electromagnetic flow meters generally use alternating magnetic fields and are excited by a 50HZ power supply.

Measurement catheter: Its function is to allow the measured 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 material, it is the outer shell 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.

Characteristics of liquid electromagnetic flowmeter

1. Measurement is not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;
2. There are no obstructing flow components or pressure loss inside the measuring tube, and the requirements for straight pipe sections are relatively low. Has unique 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, stable zero point, and high accuracy. 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, 2×16 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 the latest and most advanced international 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 high-quality materials to ensure the stability of product performance over a long period of time.

Liquid electromagnetic flowmeter classification

According to the different types of applied magnetic field, electromagnetic flowmeters mainly have two kinds of direct flow and induction. The applied constant lower magnetic field B of the direct-flow electromagnetic current (FIG. 2) is perpendicular to the tube axis, and two electrodes are installed at C and D to measure the electromotive force U induced by the fluid crossing the magnetic field.
Where A is the cross-sectional area of the pipeline; d is the diameter of the pipe; k is the correction factor, which is used to correct for the influence of factors not taken into account in the derivation of the formula (such as the fact that the flow rate in the flowmeter pipe is not uniform). In a normal flowmeter, k is about 0.8, but for a specific size, electromagnetic flowmeter for a specific working condition, the volume method (volume of flow in a certain time) should be used to calibrate the k value. The magnetic field can be generated by a permanent magnet, usually an aluminum-nickel-cobalt alloy. When the flow rate is large, because of the large diameter of the pipe, the core-free exciting winding is used to generate an approximate uniform magnetic field through the direct current.
Induction electromagnetic flowmeter can be used when the temperature of the measured flow is too high or has a strong corrosion effect on the electrode. A and B are two AC excitation windings with equal turns (cross-section is drawn in the figure), and the windings are connected in series, but their respective current directions are opposite. When the fluid is at rest, the resultant flux through the induction coil C is zero, so there is no induced alternating electromotive force in the coil. Alternating electromotive force is generated in the induction coil when the fluid flows, and its magnitude is proportional to the flow rate. Based on this principle, there are many variants. For example, an exciting winding is used, and an induction coil in the opposite direction is placed on each side of its symmetry and connected in series (Figure 3) when the fluid flows, the magnetic field line moves in the direction of flow, so that the generated electromotive force in the induction coil on both sides is not zero, which can indirectly indicate the size of the flow rate.
There are no other parts in the pipeline of the electromagnetic flowmeter, so in addition to measuring the flow of conductive fluids, it can also be used to measure the flow of non-conductive liquids of various viscosities (in which easily ionized substances are added). Electromagnetic flowmeters are often used in the nuclear energy industry.

Electromagnetic flowmeter on the display mode is divided into: component type electromagnetic flowmeter, a type electromagnetic flowmeter. Series nominal diameter DN15 ~ DN3000.
Fractional electromagnetic flowmeter is a kind of induction instrument that measures the volume flow of conductive medium in tubes according to Faraday’s electromagnetic induction law. It adopts single-chip embedded technology to realize digital excitation, and adopts CAN fieldbus on the electromagnetic flowmeter. It is the first in China and the technology has reached the leading level in China.
While meeting the on-site display, the electromagnetic flowmeter can also output 4 ~ 20mA current signal for recording, regulation and control, and has been widely used in chemical industry, environmental protection, metallurgy, medicine, paper making, water supply and drainage and other industrial technology and management departments.
In addition to measuring the flow of general conductive liquid, the electromagnetic flowmeter can also measure the liquid solid two-phase flow, high viscosity liquid flow and the volume flow of salt, strong acid and strong alkali liquid.
A type electromagnetic flowmeter is based on Faraday’s law of electromagnetic induction, used to measure the volume flow of conductive fluids. Because of its unique characteristics, it has been widely used in the measurement of various conductive liquids in industry. Mainly used in chemical industry, paper making, food, textile, metallurgy, environmental protection, water supply and drainage and other industries, with computer matching can achieve system control.
one Electromagnetic flowmeter has no moving parts, no choke parts, will not cause pressure loss, but also will not cause wear, blocking and other problems.

2. Electromagnetic flowmeter is a volume flow measuring instrument, which is not affected by the temperature, viscosity, density and conductivity (within a certain range) of the measured medium during the measurement process.
3. The electromagnetic flowmeter has a wide range, up to 1:100. In addition, the electromagnetic flowmeter is only proportional to the average flow rate of the measured medium, and has nothing to do with the axisymmetric flow state (laminar or turbulent).
4. The electromagnetic flowmeter has no mechanical inertia, is sensitive, can measure the instantaneous pulsating flow rate, and the linearity is good, so the measurement signal can be directly converted into a linear standard signal output by the converter. The LD-T type can be indicated locally, and the LD type can be transmitted remotely.