SBG257 Germany IFM electromagnetic flowmeter working principle

Working principle of the SBG257 German IFM electromagnetic flowmeter:

The German IFM electromagnetic flowmeter is a flowmeter that measures flow based on Faraday's law of electromagnetic induction. The advantage of the German IFM electromagnetic flowmeter is that the pressure loss is extremely small and the measurable flow range is large. The ratio of the maximum flow rate to the minimum flow rate is generally more than 20:1. It is suitable for a wide range of industrial pipe diameters, up to 3m. The output signal is linear with the measured flow rate. It has high accuracy and can measure conductivity ≥5μs/cm. Fluid flow of acids, alkalis, salt solutions, water, sewage, corrosive liquids, and mud, pulp, pulp, etc. But it cannot measure the flow of gas, steam and pure water.

When a conductor moves cutting magnetic field lines in a magnetic field, an induced electric potential will be generated in the conductor. The size of the induced electric potential depends on the effective length of the conductor in the magnetic field and the direction of movement of the conductor perpendicular to the direction of the magnetic field. Directly proportional to speed. In the same way, when the conductive fluid flows in the vertical direction in the magnetic field and cuts the magnetic induction force lines, it will also generate an induced electric potential on the electrodes on both sides of the pipe. The direction of the induced electric potential is determined by the right-hand rule, and the magnitude of the induced electric potential is determined by the following formula:

Ex=BDv Formula (1)

Where Ex—induced electric potential, V;

B—magnetic induction intensity, T

D—pipe inner diameter, m

v—average flow velocity of liquid, m/s

However The volume flow rate qv is equal to the product of the fluid flow rate v and the cross-sectional area of ​​the pipe (πD²)/4. Substituting equation (1) into this equation, we get:

Qv=(πD/4B)* Ex equation (2)

It can be seen from the above formula that when the pipe diameter D is fixed and the magnetic induction intensity B is kept constant, the measured volume flow rate and the induced potential have a linear relationship. If an electrode is inserted on both sides of the pipe, the induced potential Ex can be introduced. By measuring the magnitude of this potential, the volume flow rate can be obtained.

According to Faraday's electromagnetic induction principle, a pair of detection electrodes are installed on the tube wall perpendicular to the axis of the measuring tube and the magnetic field lines. When the conductive liquid moves along the axis of the measuring tube, the conductive liquid cuts the magnetic field lines to generate an induced electric potential. , this induced potential is detected by two detection electrodes, and the value is proportional to the flow rate. Its value is:

E=B·V·D·K

In the formula: E - Induced electric potential;

K - Coefficient related to magnetic field distribution and axial length;

B - Magnetic induction intensity;

V - Average flow velocity of conductive liquid;

D-electrode spacing; (measuring the inner diameter of the tube)

The sensor transmits the induced potential E as a flow signal to the converter. After signal processing such as amplification, transformation and filtering, it is processed with a band Backlit dot matrix LCD displays instantaneous flow and cumulative flow. The converter has 4~20mA output, alarm output and frequency output, and is equipped with RS-485 and other communication interfaces, and supports HART and MODBUS protocols.

German IFM electromagnetic flowThe meter is simply composed of a flow sensor transmitter. The installation requirement of German IFM electromagnetic flowmeter is that it must be installed at the low point of the pipeline or the vertical section of the pipeline, but it must be when the pipe is full. The requirement for the straight pipe section is 5D in the front and 3D in the back, so as to ensure the electromagnetic flow rate. The use of meters and the requirements for accuracy.

The structure of the German IFM electromagnetic flowmeter is mainly composed of magnetic circuit system, measuring catheter, electrode, shell, lining and converter.

Magnetic circuit system: Its function is to generate a uniform DC or AC magnetic field. The DC magnetic circuit is implemented with magnets. Its advantage is that the structure is relatively simple and is less disturbed by the AC magnetic field. However, it easily polarizes the electrolyte liquid passing through the measurement catheter, causing the positive electrode to be surrounded by negative ions and the negative electrode to be surrounded by positive ions. , that is, the polarization phenomenon of the electrodes, and causes the internal resistance between the two electrodes to increase, thus seriously affecting the normal operation of the instrument. When the diameter of the pipe is large, the magnet is correspondingly large, bulky and uneconomical, so electromagnetic flowmeters generally use alternating magnetic fields and are generated by 50HZ power frequency power supply.

Measuring catheter: Its function is to allow the conductive liquid to be measured to pass through. In order to cause the magnetic flux to be shunted or short-circuited when the magnetic lines of force pass through the measuring conduit, the measuring conduit must be made of materials that are non-magnetic, have low electrical conductivity, low thermal conductivity and have a certain mechanical strength. Non-magnetic stainless steel, glass fiber reinforced plastics, and high-strength materials can be used. Plastic, aluminum, etc.

Electrode: Its function is to elicit an induced potential signal that is proportional to the measured value. The electrodes are generally made of non-magnetic stainless steel and are required to be flush with the lining so that fluid can pass through unimpeded. Its installation position should be in the vertical direction of the pipe to prevent sediment from accumulating on it and affecting the measurement accuracy.

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

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

Converter: The induced potential signal generated by the liquid flow is very weak and is 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 it. 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.