electromagnetic flowmeter

LDCK Electromagnetic flowmeters (EMF) is the 20th century, 50 ~ 60 years with the development of electronic technology and the rapid development of new flow measurement instruments. Electromagnetic flowmeter is the application of electromagnetic induction principle, according to the conductive fluid through the magnetic field when the induced electromotive force to measure the flow of conductive fluid of an instrument.

Introduction to the instrument

structure

The structure of the electromagnetic flowmeter produced by shanghai automation instrumentation co., ltd. is mainly composed of magnetic circuit system, measuring pipe, electrode, shell, lining and converter.

Magnetic circuit system: its role is to produce a uniform DC or AC magnetic field. DC magnetic circuit with permanent magnets to achieve, the advantage of the structure is relatively simple, by the AC magnetic field interference is small, but it is easy to measure the conductivity of the electrolyte through the catheter, the positive electrode is surrounded by negative ions, the negative electrode is positive ions Surrounded by the polarization of the electrode, and lead to increased resistance between the two electrodes, which seriously affect the normal work of the instrument. When the pipe diameter is larger, the permanent magnet is also a large, cumbersome and uneconomical, so the electromagnetic flowmeter generally use alternating magnetic field, and is 50HZ power frequency excitation generated.

Measuring catheter: its role is to allow the conductivity of liquid through. In order to make the magnetic flux through the measurement of the catheter when the flux is shunt or short circuit, the measurement of the catheter must be non-magnetic, low conductivity, low thermal conductivity and a certain mechanical strength of the material made of non-magnetic stainless steel, glass steel, Plastic, aluminum and so on.

Electrode: Its role is to lead out and be measured in proportion to the induced potential signal. The electrodes are generally made of non-magnetic stainless steel and are required to be flush with the lining so that the fluid passes unobstructed. It should be installed in the vertical direction of the pipeline to prevent sediment accumulation in the above and affect the measurement accuracy.

Shell: made of ferromagnetic material, is the distribution of the system coil coil cover, and isolation of external magnetic field interference.

Lining: On the inside of the measuring catheter and the flange sealing surface, there is a complete electrical insulation lining. It is directly in contact with the measured liquid, its role is to increase the measurement of the corrosion resistance of the catheter to prevent the induced potential of the metal pipe wall short circuit. Lining materials are mostly corrosion-resistant, high temperature, wear-resistant PTFE plastic, ceramics and so on.

Converters: The induced potential signals generated by liquid flow are very weak and are greatly influenced by various disturbances. The converter functions to amplify and convert the induced potential signals into uniform standard signals and suppress the main interfering signals. The task is to convert the induced potential signal Ex of the electrode into a unified standard DC signal.

Features

1, the measurement is not affected by fluid density, viscosity, temperature, pressure and conductivity changes;

2, the measurement tube without obstruction of moving parts, no pressure loss, straight pipe requirements lower. Has a unique adaptability to slurry measurement;

3, a reasonable choice of sensor lining and electrode materials, that is, with good corrosion resistance and wear resistance;

4, the converter uses a new excitation method, low power consumption, zero stability, high accuracy. Flow range of up to 150: 1;

5, the converter can be integrated with the sensor or separation type;

6, the converter uses 16-bit high-performance microprocessors, 2x16LCD display, parameter settings convenient, reliable programming;

7, flow meter for the two-way measurement system, built-in three totalizer: positive total, reverse total and the difference between the total; can display positive and negative flow, and has a variety of output: current, pulse, digital communication , HART;

8, the converter using surface mount technology (SMT), with self-test and self-diagnostic function;

9, the measurement accuracy from the fluid density, viscosity, temperature, pressure and conductivity changes, the sensor induced voltage signal and the average flow rate was linear, so the measurement accuracy.

10, measuring the pipe without resistance flow, so there is no additional pressure loss; measuring the pipe without moving parts, so the sensor life is extremely long.

11, because the induced voltage signal is formed in the entire field filled with magnetic field, is the average on the surface of the pipeline, so the sensor required straight pipe section is shorter, the length of 5 times the pipe diameter.

12, the converter using the latest international most advanced single-chip (MCU) and surface mount technology (SMT), reliable performance, high precision, low power consumption, zero stability, easy to set parameters. Click the Chinese display LCD, show the cumulative flow, instantaneous flow, flow rate, flow percentage and so on.

13, two-way measurement system, measurable forward flow, reverse flow. Using a special production process and high-quality materials to ensure that the performance of the product in a long time to maintain stability.

classification

According to the different types of magnetic field, electromagnetic flowmeter mainly DC and induction type two. The external constant magnetic field B of the DC-type electromagnetic dissipator (Fig. 2) is perpendicular to the tube axis, and two electrodes are provided at C and D to measure the electromotive force U induced when the fluid crosses the magnetic field. The flow Q can be found by:

Where A is the cross-sectional area of ??the pipe; d is the pipe diameter; k is the correction factor, which is used to correct the factors that are not taken into account when the derivation formula (such as the flow rate in the flow meter pipe is not evenly). In a conventional flowmeter, k is about 0.8, but for a specific size, the electromagnetic flowmeter for a specific operating condition is used to calibrate the k value using the volumetric method (the volume that flows over a certain period of time). The magnetic field can be produced by permanent magnets, which are generally aluminum-nickel-cobalt alloys. When the flow is large, because of the larger diameter, so the use of non-core excitation winding, through its often DC current to produce an approximate uniform magnetic field.

Inductive electromagnetic flowmeter in the measured fluid temperature is too high or the electrode has a strong role in corrosion, etc., can be used inductive electromagnetic flowmeter (Figure 2). A, B for the two turns equal to the two AC excitation winding (the picture is the cross section), the windings are connected in series, but the current direction of the opposite. When the fluid is stationary, the synthetic magnetic flux through the induction coil C is zero, so there is no induced alternating electromotive force in the coil. When the fluid flows, the induced electromotive force is generated in the induction coil, and its size is proportional to the flow rate. Based on this principle, there are many modifications. For example, with an excitation winding, and in its symmetrical sides placed on the opposite side of the opposite direction of the induction coil and connected in series (Figure 3) fluid flow, the magnetic force lines to move the direction of movement, so that both sides of the induction coil in the surprising electromotive force is not Zero, which can indirectly indicate the size of the flow.

There is no other part in the pipe of the electromagnetic flowmeter, so it can be used to measure the flow of nonconductive liquids of various viscosities (in which the ionizable substance is added) in addition to the flow rate used to measure the conductive fluid. In the nuclear industry often use electromagnetic flowmeter.

Electromagnetic flowmeter on the display is divided into: split electromagnetic flowmeter, integrated electromagnetic flowmeter. Series Nominal diameter DN15 ~ DN3000.

Split electromagnetic flowmeter is a kind of according to Faraday's law of electromagnetic induction to measure the volume flow of conductive medium in the tube of induction instrument, the use of single-chip embedded technology to achieve digital excitation, while the use of electromagnetic flowmeter CAN field bus, is a domestic initiative, Technology to achieve the leading domestic level.

Split electromagnetic flowmeter to meet the field display at the same time, you can also output 4 ~ 20mA current signal for recording, regulation and control, has been widely used in chemical, environmental protection, metallurgy, medicine, paper, water supply and drainage and other industrial technology and Management department.

Split electromagnetic flowmeter in addition to measuring the flow of general conductive liquid, but also measure the liquid-solid two-phase flow, high viscosity liquid and salt, strong acid, alkali liquid volume flow.

The integrated electromagnetic flowmeter is based on Faraday's law of electromagnetic induction to measure the volume flow of conductive fluids. Because of the unique characteristics have been widely used in a variety of industrial conductive liquid measurement. Mainly used in chemical industry, paper, food, textile, metallurgy, environmental protection, water supply and drainage and other industries, and computer support system control can be achieved.

1. Electromagnetic flowmeter no moving parts, there is no blocking flow, will not cause pressure loss, but also does not cause wear, blocking and other issues.

2. The electromagnetic flowmeter is a volumetric flow meter that is not affected by the temperature, viscosity, density, and conductivity (within a certain range) of the medium under test.

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

4. Electromagnetic flowmeter without mechanical inertia, responsive, can measure the instantaneous pulsating flow, and good linearity, so you can measure the signal directly with the converter linear conversion into a standard signal output. LD-T type can be local instructions, LD type can be long-distance transmission.