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Introduction to the development direction of electromagnetic flowmeter technology

Electromagnetic flowmeter skills development process:
From the exchange of sinusoidal power frequency excitation in the 1950s to the low-frequency rectangular wave excitation that emerged in the 70s and 80s, and then to the high-frequency excitation, dual-frequency excitation, programmable master excitation, etc. since the 1990s, the excitation method has been Improvements represent an ongoing advancement in electromagnetic flowmeter technology. With the development of electronics and computer skills, the development of electromagnetic flowmeter technology has been slowed down. The development of electromagnetic flowmeters in the future can be summarized as follows.
(1), electromagnetic flowmeter - high accuracy
Compared with the late power frequency excitation, the new excitation method electromagnetic flowmeter such as low-frequency rectangular wave excitation, dual-frequency excitation, programmable master excitation, improves the signal-to-noise ratio of the sensor input flow signal, and reduces and stabilizes the zero point of the instrument. The converter uses an advanced integrated computational reducer to drastically reduce the noise of the device. Taking a digital processing method, the converter that mimics the circuit can greatly improve the measurement accuracy of the electromagnetic flowmeter. The weighting function of the induced signal is practiced to improve the influence of the non-axis symmetry of the flow velocity distribution in the pipeline on the correct measurement of the flow. Therefore, modern electromagnetic flowmeters have measurement accuracy that can reach ±0.5% or even ±0.2% indication error.
(2), electromagnetic flowmeter - high reliability, multi-function
The zero point change of the flowmeter is important because in the metal measuring tube and the conductive liquid in the alternating task magnetic field, even if the fluid flow rate is zero, the eddy current will still occur due to the electromagnetic induction, and the secondary magnetic flux is formed. . The low-frequency rectangular wave excitation energy effectively increases the occurrence of secondary magnetic flux, so the zero point is relatively stable. The frequency of the rectangular wave magnetic field is an integer multiple of the power frequency. When the signal is sampled, its uniform value is zero, which can eliminate the influence of power frequency frame mode disturbance. Modulated dual-frequency excitation and programmable master excitation can reduce the influence of low-frequency electrochemical noise on the electrode when measuring the flow of solid-liquid two-phase slurry, and improve the reliability of the sensing signal. Highly integrated electronic components add hardware failure rates, hardware and software shielding techniques, etc., are all effective ways to add converter reliability.
The single-chip computer in the converter can fully utilize the advantages of information storage, time-sharing, calculation and mastery of the computer. It can easily complete the two-way measurement of flow, full-tube detection, multi-range active switching, man-machine Additional functions such as dialogue, communication with the upper computer, and self-diagnosis. A new generation of electromagnetic flowmeters with HART protocol and the remaining types of fieldbus provides users with new conditions for consumer control and scientific governance.
(3), electromagnetic flowmeter - miniaturization
The electromagnetic flow sensor of the weight-distributed magnetic field has a magnetic field coil that is more evenly distributed. The length of the magnetic field excitation coil is greatly prolonged; the improvement of the low-frequency excitation signal-to-noise ratio can also greatly reduce the magnetic induction intensity. Therefore, the coil core size can be reduced and the length of the sensor can be extended. Therefore, compared with the advanced electromagnetic flowmeter, the later electromagnetic flowmeter can complete the miniaturization of the product. The integrated structure of the sensor and the converter is combined to effectively reduce the production of the flowmeter.
(4), electromagnetic flowmeter - low energy consumption
In the late exchange excited electromagnetic flowmeter, there is a large eddy current loss. In order to obtain high measurement accuracy, a strong induced electromotive force is required. At this time, the designed sensor magnetic field is about 1 to 2 mV of induced signal voltage at a flow rate of Im/s. Therefore, the exchange excitation type electromagnetic flowmeter consumes power in the range of tens of watts to kilowatts. The low-frequency rectangular wave magnetic field is in a direct current state, and its core eddy current loss is small, and the magnetic induction intensity is very low. The sensor magnetic field designed in this way is probably an induced signal voltage of 0.1 to 0.2 mV at a flow rate of Im/s. Therefore, the electromagnetic flowmeter excited by the low-frequency rectangular wave is significantly reduced in energy consumption compared with the exchange-excited electromagnetic flowmeter. Now, the total power consumption of individual electromagnetic flowmeters is within 10~20W. A two-wire electromagnetic flowmeter with an excitation current below 4 mA has also emerged. It consumes only 2 mW of power and can be powered by a lithium battery for 8 years. There are also electromagnetic flowmeter products that are used without switching electricity.
(5), electromagnetic flowmeter - the expansion of practical scale
The development of modern electronic technology and new insulation materials and magnetic data have emerged. It is necessary to develop different types of electromagnetic flowmeters to deal with the erosion and purification of the measuring medium, and to measure the conductivity of materials below 1μS/m. For example, a capacitive electromagnetic flowmeter can replace a conventional mechanical volumetric flowmeter to measure the flow of pure water, sugar-salted desalting liquid, and low-conductivity fluids containing oil.
There are many varieties of electromagnetic flowmeters, and they are widely used. For example, the sensor and converter structure are integrated into one, the two-wire system of DC voltage supply and signal input shared cable, explosion-proof type, low-pressure sensor structure type, suitable for hygienic request, for disinfection of rapid device and assembly Type, with digital communication signal input function, etc., they are increasingly popular in the chemical, petroleum, steel, metallurgy, food and other industries to actively grasp the consumption process.
In addition to the flowmeters used by submersible electromagnetic flowmeters to measure rivers, culverts and open channels, electromagnetic flowmeters for non-full pipes are also hot products developed in recent years. In today's environmental protection and water conservation are increasingly concerned, they play a serious role in the measurement of low-flow open channels, culvert water, sewage.
The food industry, pharmaceutical consumption or canning, requesting quantitative measurement and recovery of the mastery signal in a short time; for blood and pulsating flow measurements, requesting a fast response. These requests need to be handled by excitation methods such as high frequency or dual frequency. In short, the new scope of application has been expanding, and will continue to make progress and progress in electromagnetic flowmeter technology.

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