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Description of the requirements of electromagnetic flowmeter application site

Requirements for the application of electromagnetic flowmeters Since the 1970s, there has been a key-controlled low-frequency rectangular wave excitation method, which has gradually replaced the industrial frequency AC excitation method of early application. The performance of the instrument has been greatly improved and it has been widely used. A wide range of applications. Large-diameter instruments are mostly used in water supply and drainage projects. Medium and small calibers are often used for solid-liquid double equal unpredictable fluids or high-demand places, such as paper pulp and black liquor in the paper industry, pulp in non-ferrous metallurgical industry, coal slurry in coal preparation plant, strong corrosive liquid in chemical industry, and blast furnace tuyere in steel industry. Cooling water control and monitoring, flow measurement and control of hydraulic conveying of long-distance pipeline coal. Small caliber and small caliber are often used in places with hygienic requirements such as the pharmaceutical industry, food industry, and bioengineering.
The electromagnetic flowmeter consists of two parts: the flow sensor and the converter. The oil flowmeter sensor has a typical structure. The measuring tube is provided with an exciting coil on the upper and lower sides of the measuring tube. After the exciting current is generated, a magnetic field is generated to pass through the measuring tube. A pair of electrodes are mounted on the inner wall of the measuring tube to contact the liquid, and the induced potential is extracted and sent to the converter. The excitation current is supplied by the converter. The electromagnetic flowmeter is a meter that measures the volumetric flow of the conductive liquid using Faraday's law of electromagnetic induction. In the early 1950s, industrial applications were realized. In recent years, worldwide production accounts for about 5% to 6.5% of the number of industrial flow meters.
Electromagnetic flowmeters are used in a wide range of applications. Oil flowmeters are available in large diameter, medium and small diameter, small diameter and small diameter according to the application. Large diameter electromagnetic flowmeters are mostly used in water supply and drainage projects. Medium and small diameters are often used in solid-liquid double equal unsuitable fluids or high-demand places. For example, measuring pulp and black liquor in paper industry, pulp in non-ferrous metallurgy industry, coal slurry in coal preparation plant, strong corrosive liquid in chemical industry, cooling water control in blast furnace tuyere of steel industry, and hydraulic flow measurement of long-distance pipeline coal Control, etc., and small caliber and small caliber are often used in places with hygienic requirements such as the pharmaceutical industry, food industry, and bioengineering.
When measuring the fluid that is easy to adhere to and deposit substances on the pipe wall, if the conductive material is higher than the conductivity of the liquid, the signal potential will be short-circuited and will not work. If it is a non-conductive layer, the electrode contamination should be paid attention first. Attach a pointed or hemispherical protruding electrode, a replaceable electrode, a scraper type cleaning electrode, and the like. The scraper electrode can be manually scraped off the scale manually outside the sensor. Foreign products have been equipped with ultrasonic transducers on the electrodes to remove surface scale, but it is now rare. There is also a temporary disconnection of the measuring circuit, a low-voltage large current flows in a short period of time, and incineration removes the adhesion layer attached to the grease. The place where the adhesion is easy can be increased to achieve the purpose of self-cleaning, and a convenient and easy-to-clean pipe connection can be adopted, and the cleaning sensor can be removed.
Some models claim to have higher accuracy, the basic error is only (±0.2% ~ ±0.3%) R, but there are strict installation requirements and reference conditions, such as ambient temperature 20 ~ 22 ° C, the length of the straight pipe length before and after the requirements More than 10D and 3D, it is even suggested that the flow sensor should be integrated with the front and rear straight tubes for real-flow calibration on the flow standard device to reduce the impact of the clamping. Therefore, do not simply look at high indicators when comparing multiple models. As one of the industrial flow measuring instruments, the electromagnetic flowmeter has some skills and precautions in its selection. Here, I combine some of my personal experience and discussion, and hope to contribute to the correct selection of electromagnetic flowmeter.

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