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| add time： | 2016-01-18 09:09:27 |
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Electromagnetic flowmeter is a new type of flow measuring instrument developed rapidly with the development of electronic technology in the 50~60's in twentieth Century. Electromagnetic flowmeter is a kind of instrument for measuring the flow of conductive fluid based on the principle of electromagnetic induction.
structure
The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring tube, an electrode, a shell, a lining and a converter.
Magnetic circuit system: its function is to produce a uniform DC or AC magnetic field. DC magnetic circuit by using permanent magnet to achieve, the utility model has the advantages of is relatively simple structure, less interference by AC magnetic field, but it is easy to make by catheter for measurement of liquid electrolyte polarization, the positive electrode was negative ion surrounded, negative electrode is positive ion surrounded, the polarization of electrode and lead to between two electrode resistance increases, and seriously affect the normal work of the instrument. When the diameter of the pipe is larger, the permanent magnet is correspondingly large, bulky and not economical, so the electromagnetic flowmeter is generally adopted by the alternating magnetic field, and the 50HZ power source excitation is produced.
Measurement of the catheter: its role is to allow the conductive liquid to be measured by. To the magnetic field through catheter for measurement of magnetic flux is diverted or short circuit, catheter measurements must use no magnetic conduction, low conductivity, low heat conduction rate and has a certain mechanical strength of materials, and can be selected non magnetic stainless steel, glass steel, high strength plastic, aluminum and other.
Electrode: its function is to draw out and to be measured directly proportional to the induced electric potential signal. Electrodes are made of stainless steel, which are generally non - magnetic, and are required to be flush with the lining so that the fluid is not obstructed. Its installation position should be in the vertical direction of the pipeline to prevent sediment accumulation in the above and affect the accuracy of the measurement.
The shell made of ferromagnetic material is used, the housing distribution system of the excitation coil, the magnetic field interference and isolation.
Lining: in the measurement of the inner and flange sealing surface of the pipe, there is a layer of complete electrical insulation lining. It is directly contacted with the liquid to be measured, the function of which is to increase the corrosion resistance of the measuring conduit and to prevent the electric potential from being short of the pipe wall. Lining materials for corrosion resistance, high temperature, wear-resistant PTFE plastic, ceramics, etc..
Converter: produced by the liquid flow induction electromotive force signal is very weak, by the influence of various interference factors, converter is the induction electromotive force signal is amplified and converted into a unified standard signal and suppress the interference signal. The task is to detect the induction potential of the electrode signal Ex amplified converted into a unified standard DC signal.
characteristic
1, the measurement is not affected by fluid density, viscosity, temperature, pressure and conductivity changes;
2, the measurement of the flow of the pipe without obstruction, without pressure loss, straight pipe section requires low. Has the unique adaptability to the slurry measurement;
3, reasonable choice of sensor lining and electrode material, which has good corrosion resistance and wear resistance;
4, the converter uses the novel excitation mode, the power consumption is low, the zero point is stable, the precision is high. Flow range up to 150:1;
5, the converter can be composed of a body or a separate type of sensor;
6, the converter uses 16 bit high performance microprocessor, 2x16LCD display, the parameter setting is convenient, the programming is reliable;
7, a flowmeter for bidirectional measurement system, in which three integrator: forward total, reverse total and the difference between the total; can display the positive and reverse flow, and has a variety of output: current, pulse, digital communications, Hart.
8, the converter uses the surface mount technology (SMT), has the self inspection and the self diagnosis function;
9, the measurement accuracy is not affected by the density, viscosity, temperature, pressure and conductivity of the sensor, the sensor voltage signal and the average flow rate is linear, so the measurement accuracy is high.
10, measuring the pipeline without resistance, so there is no additional pressure loss; measurement of the pipeline without moving parts, so the sensor life is very long.
11, due to the induction voltage signal is formed in the space of the full magnetic field, is the average value of the pipeline on the surface, so the required straight pipe section of the sensor is short, the length of 5 times the diameter of the pipe.
12, converter using the latest international most advanced single chip (MCU) and surface mount technology (SMT), reliable performance, high precision, low power consumption, stable zero, convenient parameter setting. Chinese display LCD, display the cumulative flow, instantaneous flow, flow rate, flow rate, etc..
13, two-way measurement system, can be measured forward flow, reverse flow. Adopt special production process and high quality materials to ensure the stability of the product in a long time.
classification
According to the different types of external magnetic field, electromagnetic flowmeter has two main types of DC and induction. DC electromagnetic flow dry meter (Figure 2) external constant under magnetic field B is vertical to the axis of the tube, C, d with two electrodes, used to measure the fluid across the magnetic field feel electromotive force u. Flow Q can be used to find out:
In the formula A is the pipeline cross-sectional area; the D is the pipe diameter; the K is the correction factor, which is used to modify the influence of the factors (such as the fact that the flow rate in the flow meter is not uniform). In the regular flow meter, K is about 0.8, but for the specific size of the electromagnetic flow meter for specific conditions, the volume method (a certain amount of time) to calibrate the K value. The magnetic field can be produced by the permanent magnet, and the magnet material is aluminum nickel cobalt alloy. Traffic flow, due to the larger diameter, so the coreless exciting winding, with its constant DC current to generate an approximate uniform magnetic field.
Induction type electromagnetic flowmeter can be used in the case of high temperature or strong corrosive effect on the electrode, the induction type electromagnetic flowmeter (Figure 2). A and B for equal numbers of turns of two AC excitation winding (in the picture is section), between the winding is series, but is in contrast to the respective current direction. When the fluid is stationary, the magnetic flux of the induction coil C is zero, so there is no induced alternating electromotive force in the coil. When the fluid flows, the induction coil generates an alternating electromotive force, which is proportional to the velocity of the flow. Based on this principle, there are a lot of modification. Such as an excitation winding, and on both sides of the symmetrical each placement in a direction opposite to the induction coil and connected in series (Figure 3) when the fluid flow, the lines of magnetic force to move in the direction of flow, on both sides of the induction coil in the surprise students electromotive force is not zero, thereby indirectly table showing the flow size.
There are no other parts in the electromagnetic flow meter, so it can be used to measure the flow rate of the conductive fluid, and the flow rate of the non conducting liquid (which is added with the easily ionized substance). Electromagnetic flowmeter is often used in nuclear power industry.
The electromagnetic flowmeter is divided into: sub type electromagnetic flowmeter, electromagnetic flowmeter. Series of nominal diameter DN15 ~ DN3000.
Split type electromagnetic flowmeter is a kind of according to Faraday's law of electromagnetic induction to measure tube conductive medium volume flux of induction type meter, uses the monolithic integrated circuit embedded technology, digital excitation, while using CAN field bus in the electromagnetic flowmeter, belong to domestic initiate, technology has reached the leading domestic level.
Split type electromagnetic flowmeter to meet the scene shows at the same time, also can output 4 ~ 20mA current signal for recording, regulation and control, has extensive application in chemical industry, environmental protection, metallurgy, medicine, paper making, to drainage of industrial technology and management.
Sub type electromagnetic flowmeter in addition to the measurement of conductive liquid flow, and can also measure solid-liquid two-phase flow, volume flow of high viscosity liquid flow and the salts, acid and alkali liquid.
An electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction, which is used to measure the volume flow of conducting fluid. The unique characteristics have been widely used in the measurement of all kinds of conductive liquid in industry. Mainly used in chemical, paper, food, textile, metallurgy, environmental protection, water supply and drainage and other industries, and the computer can realize the system control.
1 electromagnetic flowmeter without moving parts, there is no resistance flow, will not cause the pressure loss, but also will not cause wear, blocking and other issues.
2 electromagnetic flowmeter is a volume flow measuring instrument, the measuring process is not affected by the temperature, viscosity, density and conductivity of the media (in a certain range).
3 the range of the electromagnetic flowmeter is wide, up to 1:100. In addition, the electromagnetic flowmeter is only proportional to the mean velocity of the measured medium, and is independent of the axial symmetrical flow state (laminar or turbulent flow).
4 electromagnetic flowmeter without mechanical inertia, the reaction is sensitive, can measure the instantaneous pulse flow, and linear good, so the measured signal can be directly converted into a linear standard signal output. LD-T type can be in situ instructions, LD type can be transmitted over a long distance.
