The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring conduit, an electrode, a casing, a lining, and a converter.
Magnetic circuit system: its role is to produce a uniform DC or AC magnetic field. The DC magnetic circuit is realized by a permanent magnet, which has the advantages of simple structure and less interference by the alternating magnetic field, but it is easy to polarize the electrolyte liquid in the measuring catheter, so that the positive electrode is surrounded by negative ions, and the negative electrode is positive The ion enveloping, that is, the polarization phenomenon of the electrode, causes an increase in internal resistance between the two electrodes, thus seriously affecting the normal operation of the meter. When the diameter of the pipe is large, the permanent jiu magnet is also large, bulky and uneconomical, so the electromagnetic flowmeter generally adopts an alternating magnetic field and is generated by the excitation of a 50HZ power frequency power source.
Measuring catheter: its function is to let the conductive liquid to be tested pass. In order to make the magnetic flux diverted or short-circuited when the magnetic flux passes through the measuring catheter, the measuring catheter must be made of non-magnetic, low electrical conductivity, low thermal conductivity and mechanical strength. Non-magnetic stainless steel, FRP, high strength can be used. Plastic, aluminum, etc.
Electrode: Its function is to extract and induce a proportional induced inductive potential signal. The electrodes are typically made of non-magnetically conductive stainless steel and are required to be flush with the liner so that the fluid passes unimpeded. It should be installed in the vertical direction of the pipe to prevent deposits from accumulating on it and affecting the measurement accuracy.
Enclosure: Made of ferromagnetic material, it is the cover of the distribution system excitation coil and isolates the interference of external magnetic field.
Lining: A complete electrical insulation lining on the inside of the measuring tube and on the flange sealing surface. It directly contacts the liquid to be measured, and its function is to increase the corrosion resistance of the measuring catheter and prevent the induced potential from being short-circuited by the metal measuring tube wall. Most of the lining materials are PTFE plastics and ceramics that are resistant to corrosion, high temperature and wear.
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 the main interference signal. Its task is to amplify the induced potential signal Ex detected by the electrode into a unified standard DC signal.
In order to make the electromagnetic flowmeter work stably and reliably, the following aspects should be noted when selecting the installation location:
1. Try to avoid ferromagnetic objects and equipment with strong electromagnetic fields (large motors, large transformers, etc.) to prevent the magnetic field from affecting the working magnetic field and flow signal of the sensor.
2. It should be installed in a dry and ventilated place to avoid sun and rain. The ambient temperature should be -20~+60°C, and the relative humidity is less than 85%.
3. There should be plenty of space around the flowmeter for easy installation and maintenance.
Installation suggestions:
The measurement principle of the electromagnetic flowmeter does not depend on the characteristics of the flow. If there is a certain turbulence and vortex in the pipeline, it will be generated in the non-measurement zone (such as elbow, tangential current limit or half-opening shut-off valve upstream). Nothing.
If steady-state eddy currents in the measurement zone affect the stability of the measurement and the accuracy of the measurement, then some measures should be taken to stabilize the flow rate distribution:
a.increase the length of the straight pipe before and after; b. use a flow stabilizer; c. reduce the cross section of the measuring point.
The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring conduit, an electrode, a casing, a lining, and a converter.
Magnetic circuit system: its role is to produce a uniform DC or AC magnetic field. The DC magnetic circuit is realized by a permanent magnet, which has the advantages of simple structure and less interference by the alternating magnetic field, but it is easy to polarize the electrolyte liquid in the measuring duct, so that the positive electrode is surrounded by negative ions, and the negative electrode is positive ion Surrounding, that is, the polarization phenomenon of the electrode, and causing an increase in internal resistance between the two electrodes, thus seriously affecting the normal operation of the meter. When the diameter of the pipe is large, the permanent magnets are correspondingly large, bulky and uneconomical, so the electromagnetic flowmeter generally adopts an alternating magnetic field and is generated by the excitation of a 50HZ power frequency power source.
Measuring catheter: its function is to let the conductive liquid to be tested pass. In order to make the magnetic flux diverted or short-circuited when the magnetic flux passes through the measuring catheter, the measuring catheter must be made of non-magnetic, low electrical conductivity, low thermal conductivity and mechanical strength. Non-magnetic stainless steel, FRP, high strength can be used. Plastic, aluminum, etc.