Internal structure of a magnetic flow meter

　　Magnetic Circuit System: Its function is to generate a uniform DC or AC magnetic field. DC magnetic circuits use permanent magnets, which have the advantages of simpler structure and lower sensitivity to AC magnetic field interference. However, they easily polarize the electrolyte liquid in the measuring tube, resulting in the positive electrode being surrounded by negative ions and the negative electrode being surrounded by positive ions, i.e., electrode polarization. This leads to an increase in the internal resistance between the two electrodes, seriously affecting the normal operation of the instrument. When the tube diameter is larger, the permanent magnet is also correspondingly larger, making it bulky and uneconomical. Therefore, electromagnetic flow meters usually use an alternating magnetic field generated by a 50Hz power supply.

　　Measuring Tube: Its function is to allow the conductive liquid to be measured to pass through. In order to prevent magnetic flux leakage or short circuit when magnetic lines of force pass through the measuring tube, the measuring tube must be made of non-magnetic material with low conductivity, low thermal conductivity and sufficient mechanical strength. Non-magnetic stainless steel, glass fiber, high-strength plastic and aluminum can be used.

　　Electrodes: Their function is to output an induced electromotive force signal proportional to the measured value. Electrodes are usually made of non-magnetic stainless steel and need to be flush with the liner to avoid obstructing fluid flow. Their installation position should be perpendicular to the pipe to prevent sediment accumulation on them, affecting the measurement accuracy.

　　Housing: Made of ferromagnetic material, it acts as a housing for the excitation coil and isolates interference from external magnetic fields.

　　Liner: There is a complete electrical insulation liner inside the measuring tube and on the flange sealing surface. It is in direct contact with the liquid to be measured, and its function is to improve the corrosion resistance of the measuring tube and prevent the induced electromotive force from being shorted by the metal measuring tube wall. The liner material is mainly corrosion-resistant, high-temperature-resistant, and wear-resistant polytetrafluoroethylene plastic, ceramics, etc.

　　Converter: The induced electromotive force signal generated by liquid flow is very weak and is greatly affected by various interference factors. The function of the converter is to amplify the induced electromotive force signal and convert it into a unified standard signal, suppressing the main interference signals. Its task is to amplify the induced electromotive force signal Ex detected by the electrodes and convert it into a unified standard DC signal.