Development history of electromagnetic flowmeter

　　Electromagnetic flowmeter is a new type of flow measurement instrument that developed rapidly in the 1950s and 1960s with the development of semiconductor technology and electronic technology. In the 1970s and 1980s, electromagnetic flow had a major breakthrough in technology, making it a widely used type of flowmeter. Since the flow signal obtained in the electromagnetic flowmeter sensor is very weak (usually at the mV or uV level), the flow signal is easily obliterated by various on-site interference signals, so the development of electromagnetic flowmeter is closely related to the development and progress of anti-interference technology.

　　Early electromagnetic flowmeters mainly measured the flow velocity under a constant magnetic field or a DC excitation magnetic field, but due to the polarization effect of the fluid medium and the interference noise generated by the thermoelectric effect, it was difficult for the electromagnetic flowmeter to separate the flow signal from the interference noise, so the use of electromagnetic flowmeters was very limited.

　　After World War II, in order to reduce the influence of the severe polarization potential on the electrode surface under the DC excitation magnetic field, a variety of anti-interference measures such as industrial frequency sinusoidal wave excitation technology and orthogonal interference suppression circuits were adopted, but this introduced 50hz industrial frequency interference problems such as electromagnetic induction and electrostatic coupling. The main problems of electromagnetic flowmeters during this period were that the influence of power frequency interference noise could not be completely eliminated, the zero point was difficult to stabilize, the measurement accuracy was low, and the reliability was poor.

　　In the mid-1970s, with the development of electronic technology and the advent of synchronous sampling technology, low-frequency rectangular wave excitation technology was adopted to change the morphological characteristics of power frequency interference, and the power frequency synchronous sampling technology was used to obtain a better ability of electromagnetic flowmeters to resist power frequency interference, improve measurement accuracy, stabilize zero point, and enhance reliability.
　　In the early 1980s, three-value low-frequency rectangular wave excitation technology and dynamic zeroing technology, synchronous excitation, and synchronous sampling technology were adopted to obtain the best zero point stability of electromagnetic flowmeters, and further improve the ability to resist power frequency interference and polarization potential interference. In the

　　early 1990s, the emergence of electromagnetic flowmeters using dual-frequency rectangular wave excitation technology, represented by ABB XM series and Yokogawa ADMAG AXF series, marked that the electromagnetic flowmeter had entered a new realm in dealing with the noise interference of the fluid itself. The dual-frequency rectangular wave excitation technology can not only overcome the mud interference and fluid flow noise generated by the fluid medium, but also have the zero point voltage stability of the low-frequency rectangular wave excitation electromagnetic flowmeter, thereby achieving the unity of the electromagnetic flowmeter's zero point stability, anti-interference ability and response speed.