Electromagnetic flowmeter technology development history

From the AC sine wave power frequency excitation developed in the 1950s to the low-frequency rectangular wave excitation in the 1970s and 1980s, and then to the high-frequency excitation, dual-frequency excitation, and programmable control excitation after the 1990s, the excitation methods are constantly changing. Improvement represents the continuous advancement of electromagnetic flowmeter technology. With the development of electronics and computer technology, the development of electromagnetic flowmeter technology has been accelerated. The current technological development of electromagnetic flowmeters can be summarized in the following aspects.
(1), electromagnetic flowmeter - high precision
Compared with the early power frequency excitation, new excitation methods such as low-frequency rectangular wave excitation, dual-frequency excitation, and programmable control excitation for electromagnetic flowmeters have improved the signal-to-noise ratio of the sensor output flow signal and reduced and stabilized the zero point of the instrument. The converter uses an advanced integrated operational amplifier to significantly reduce the noise of the device. Using the digital processing method, compared with the converter of the analog circuit, the measurement accuracy of the electromagnetic flowmeter can be greatly improved. The theoretical study of the weight function of the induction signal has improved the influence of the non-axisymmetric flow velocity distribution in the pipeline on the accurate measurement of the flow to a certain extent. Therefore, it is possible for a modern electromagnetic flowmeter to achieve a measurement accuracy of ±0.5%, or even ±0.2% of the indication error.
(2) Electromagnetic flowmeter - high reliability and multi-function
The change of the zero point of the flowmeter is mainly due to the metal measuring tube and the conductive liquid in the alternating working magnetic field. Even if the fluid flow rate is zero, the eddy current will still be generated due to the effect of electromagnetic induction, and the secondary magnetic flux will be formed. . Low-frequency rectangular wave excitation can effectively reduce the generation of secondary magnetic flux, so the zero point is more stable. The frequency of the rectangular wave magnetic field is an integer multiple of the power frequency frequency, and its average value is zero when the signal is sampled, which can eliminate the influence of power frequency series mode interference. The modulated dual-frequency excitation and programmable control excitation can reduce the influence of low-frequency electrochemical noise on the electrode when measuring the solid-liquid two-phase slurry flow, and improve the reliability of the sensing signal. Highly integrated electronic components reduce the failure rate of hardware, and shielding technology of hardware and software are all effective measures to increase the reliability of converters.
The application of a single-chip computer in the converter can make full use of the computer's advantages of information storage, time-sharing processing, calculation and control capabilities, and can easily realize two-way flow measurement, full-pipe detection, multi-range automatic switching, man-machine dialogue, Additional functions such as communication with the upper computer, self-diagnosis, etc. The new generation of electromagnetic flowmeters with HART protocol and other types of field buses provides conditions for users to realize new production control and scientific management methods.
(3), electromagnetic flowmeter - miniaturization
The length of the magnetic field coil of the electromagnetic flow sensor with weight distribution magnetic field is greatly shortened compared with that of the uniformly distributed magnetic field excitation coil; the improvement of the signal-to-noise ratio of low-frequency excitation can greatly reduce the magnetic induction intensity. Therefore, the coil core size can be reduced and the sensor length can be shortened. Therefore, compared with the earlier electromagnetic flowmeter, the current electromagnetic flowmeter can realize the miniaturization of the product. The integrated structure of the sensor and the converter can more effectively reduce the manufacturing cost of the flowmeter.
(4), electromagnetic flowmeter - low energy consumption
Early electromagnetic flowmeters with AC excitation had large eddy current losses. In order to obtain high measurement accuracy, a strong induced electromotive force needs to be generated. At this time, the designed sensor magnetic field is about the flow rate Im/s to generate an induced signal voltage of 1~2mV. Therefore, the power consumption of the AC excitation type electromagnetic flowmeter is often tens of watts to thousands of watts. The low-frequency rectangular wave magnetic field is in the DC state most of the time, the eddy current loss of the core is very small, and the magnetic induction intensity is very low. The magnetic field of the sensor designed in this way is about Im/s flow rate and can generate an induced signal voltage of 0.1~0.2mV. Therefore, compared with the AC excitation type electromagnetic flowmeter, the electromagnetic flowmeter with low frequency rectangular wave excitation has significantly lower energy consumption. Today, the total power consumption of general electromagnetic flowmeters is within l0~20W. A two-wire electromagnetic flowmeter with an excitation current below 4mA has also appeared, and an electromagnetic water meter that consumes only 2mW of power and can be used for 8 years when powered by a lithium battery. There are also electromagnetic flowmeter products that are used without alternating current.
(5) Electromagnetic flowmeter - expansion of the scope of application
With the development of modern electronic technology and the continuous emergence of new insulating materials and magnetic materials, it is possible to develop different types of electromagnetic flowmeters to solve the problem of corrosion and pollution of electrodes by measurement media, and to solve the measurement of media with conductivity lower than 1µS/m. For example, capacitive electromagnetic flowmeters can replace traditional mechanical volumetric flowmeters to measure the flow of pure water, sugar desalination liquid, and low-conductivity fluids containing oil. There are many types of electromagnetic flowmeters and they are widely used. For example, the sensor and converter structure are combined into one, the two-wire system of the DC voltage power supply and signal output shared cable, the explosion-proof type, the high-voltage sensor structure type, and the hygienic type that meets the hygienic requirements and is used for disinfection and quick installation and disassembly. , with digital communication signal output function, etc., they are more and more popular in the automatic control production process of chemical industry, petroleum, steel, metallurgy, food and other industries.
In addition to submersible electromagnetic flowmeters used to measure flowmeters in rivers, culverts and open channels, electromagnetic flowmeters for unfilled pipelines are also popular products developed in recent years. Under the circumstances that environmental protection and water saving are paid more and more attention today, they play an important role in the measurement of water and sewage in low-velocity open channels and underground channels. The food industry, pharmaceutical production or canning require quantitative measurement and sending of control signals in a short period of time; for blood and pulsation flow measurement, fast response is required. These requirements need to be solved by high-frequency or dual-frequency excitation methods. In short, the continuous expansion of new application fields will promote the continuous development and progress of electromagnetic flowmeter technology.