The working principle of the magnetic float sensor is to measure the flow rate of the conductive fluid according to the electromotive force induced when the conductive fluid passes through the external magnetic field. We knew this principle in junior high school courses, the right hand helix theorem, by cutting magnetic field lines to generate the corresponding current. The principle of the current is the electron deflection. The electrons migrate to the electrodes of the magnetic float sensor, where each electrode produces a potential difference, and then a signal outputs it. The following is a brief description of the overall composition of the magnetic float sensors for water level measuring and the corresponding role.
The structure of electromagnetic flow meter is mainly composed of magnetic circuit system, measuring conduit, electrode, enclosure, lining and converter.
Its function is to produce a uniform DC or AC magnetic field. DC magnetic circuit is realized by permanent magnet, which has the advantage of simple structure and less interference from ac magnetic field. However, it is easy to polarize the electrolyte liquid going through the measuring conduit. And then the positive electrode is surrounded by negative ions while the negative electrode is surrounded by positive ions, which is the polarization phenomenon of the electrode, and leads to the increase of internal resistance between the two electrodes, thus seriously affecting the normal operation of the instrument. When the diameter of the pipeline is large, the permanent magnet is correspondingly large, bulky and uneconomical. Therefore, the electromagnetic flow meter generally adopts alternating magnetic field and is stimulated by 50HZ power frequency power supply.
Its function is to allow the conductance liquid to pass through. The magnetic flux is shunted or short-circuited to allow the magnetic field line to pass through the measuring conduit. That's the reason the measuring conduit must be made of non-magnetic, low conductivity and low thermal conductivity materials also with certain mechanical strength. Non-magnetic stainless steel, glass fiber reinforced plastics, high-strength plastics and aluminum can be considered.
Its function is to elicit an induced potential signal that is proportional to the one being measured. The electrodes are generally made of non-magnetic stainless steel and are required to be flush with the lining, so that fluid flow is unimpeded. It should be installed in the vertical direction of the pipeline, in order to prevent sediment accumulation on it from affecting the measurement accuracy.
Made of ferromagnetic material, it is the enclosure of the excitation coil of the distribution system and isolates the interference of the external magnetic field.
There is a complete electrical insulation lining on the inner side of the measuring conduit and the flange sealing surface. It is directly in contact with the measured liquid and its function is to increase the corrosion resistance of the measuring conduit, preventing the induced potential from being short-circuited by the metal measuring conduit wall. Most of lining materials are PTFE plastics or ceramics with corrosion resistance, high temperature resistance and wear resistance.
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 the induced potential signal and convert it into a unified standard signal and at the same time, suppress the main interference signal. Its task is to amplify the induced potential signal Ex detected by the electrode and convert it into a unified standard DC signal.
The magnetic float sensors for water level measuring is based on Faraday's law of electromagnetic induction. The advantages of magnetic float sensor are that the pressure loss is very small and the measured flow range is large. The ratio of the maximum flow rate to the minimum flow rate is generally above 20:1, with a wide range of applicable industrial pipe diameter. The maximum flow is up to 3m, with the output signal linear to the measured flow and with high accuracy, which can measure the fluid flow of acid, alkali, salt solution, water, sewage, corrosive liquid, mud, ore pulp and pulp with conductivity ≥5 μs/cm. But it cannot measure the flow of gas, steam or pure water.