After many years of development, the performance of the electromagnetic flowmeter is perfect, and the function is also strong. There are a variety of classification, such as the excitation method to classify the type of DC excitation, AC frequency excitation, dual frequency excitation and low-frequency rectangular wave excitation. Is the principle of Faraday's law of electromagnetic induction, the production of a measurement of the volume flow meter.
Electromagnetic flow meter has the pressure loss is very small, the density, viscosity, temperature, pressure and other parameters of the medium are not required, and the requirements of the straight pipe section is also very low. Here is how to choose the flow meter to sit down.
1, the conductivity of the medium
The electrical conductivity of the medium can not be lower than the specified limit, if the lower bound value will produce the measurement error, which can not be used normally, and the change can be measured.
The electrical conductivity of industrial water and its aqueous solution is more than 10-4S/cm, acid, alkali, salt solution is 10-4~10-1S/cm, and the low water distilled water is 10-5S/cm, which is not a problem, for example, the electrical conductivity of petroleum products and organic solvents can not be used. The use of the water solution may be used in industrial water ratio, electrical conductivity will be slightly higher, is conducive to traffic measurement. The electrical conductivity of a number of liquids at 20 degrees C is listed below.
2, electrode materials
In the measurement of the use of the process to achieve a good measurement results, longer service life, it is necessary to test whether the fluid is corrosive to the choice of electrode material, please consult the factory corrosion manual. The following diagram is a common electrode material and the corresponding corrosion resistance.
3, measuring range
The diameter of the sensor is not necessarily the same as the diameter of the tube, and the diameter of the flowmeter must be selected according to the actual flow. For industrial transportation of water and other liquids, the general pipe flow 1.5~3m/s, electromagnetic flow meter used in such a pipeline, sensor diameter and pipe diameter can be the same.
When the flow rate of the electromagnetic flowmeter is full, the flow rate can be selected in the range of 1~10m/s. The upper limit velocity is not restricted in principle, it is recommended that no more than 5m/s, if the lining material can withstand the liquid flow erosion. The lower limit of the full flow rate is 1m/s, some type of instrument is 0.5m/s.
For easy adhesion, deposition, scaling and other substances of the fluid, the use of flow rate is not less than 2m/s, the best to improve to 3~4m/s or above, from the clean, to prevent adhesion and deposition. For a fluid slurry wear resistance, commonly used flow rate should be lower than 2~3m/s, in order to reduce the wear of the lining and the electrode. When the low conductance liquid is close to the threshold, the low flow velocity (less than 0.5~1m/s) can be selected, which will increase the flow noise, and the output will be increased.
4, containing mixture
Small bubbles that are mixed into a bubble can still work normally, but the measured volume of mixed volume flow, the gas content increases to the formation of the projectile (block), the electrode may be gas covered so that the circuit is broken off, the output can not even work.
5, the media have precipitation
Liquid easily in the tube wall adhesion and sediment of the fluid. If the attachment is higher than the liquid conductivity of conductive material, electric potential signal will be short and could not work, if non conducting layer is first of all, attention should be paid to the electrode pollution, such as the selection of not easy to be attached to the pointed or hemisphere shaped protrusion electrodes, scale electrode type electrode replacement, scraper cleaning. Easy to produce the place can improve the flow rate to achieve the purpose of self cleaning, but also can take more convenient easy to clean the pipe connection, can not remove the cleaning sensor. The contact electrode electromagnetic flow meter is attached to a non conductive film, and the meter can work, but if it is not working for the high conductive layer.
As a kind of important instrument of industrial flow measurement, electromagnetic flowmeter is fully used in the application. Has the premise of certain professional knowledge, it is necessary to master certain skills and methods on how to correct selection and installation, to meet the requirements into the enterprise management, vortex flowmeter.
