With the accelerated process of industrialization China the increasingly serious problem of environmental pollution, the voice of the community for sustainable development is more and more high, the harmony of man and nature concept is accepted, governance of pollution is more urgent. Flow measurement is very important in wastewater treatment process because of the need to measure and control the wastewater, additives, sludge and so on. Among the many flowmeter products used for sewage measurement, the electromagnetic flowmeter occupies the absolute predominance, and the accuracy is the best either in principle or in measurement.
Electromagnetic flowmeter consists of two parts: flow sensor and transmitter. A magnetic field coil is arranged between the upper and the lower of the measuring tube to generate a magnetic field through the measuring tube, and a pair of electrodes are arranged on the inner wall of the measuring tube to contact the liquid, and the induction potential is drawn to the transmitter. The excitation current is supplied by the transmitter. According to the converter and sensor assembly methods, there are two types of separation and one type. In the sewage treatment process, the large caliber flowmeter is split type, one part is installed underground, the other part is on the ground. Small caliber with one type is much. The working principle of electromagnetic flowmeter is based on Faraday electromagnetic induction law. When the conducting metal rod moves at a certain speed perpendicular to the direction of the magnetic flux line, an induced voltage is generated. If the magnetic field strength is B, the metal rod length is L, the speed is V, then the induced voltage is generated.
At present, the electromagnetic flowmeter function on the market varies greatly, simple one-way traffic on the only measure, only after driving the output analog signal level meter; intelligent electromagnetic flowmeter can measure bidirectional flow, range switching, minimum flow alarm, air traffic control and power cut off the alarm, small signal removal, the total flow rate display and calculation, automatic checking and fault diagnosis, communication with PC and motion configuration etc.. Some types of electromagnetic flowmeter, serial digital communication function, a variety of communication interface and dedicated chip (ASIC), to connect HART protocol system, PROFTBUS, Modbus, FF field bus, etc..
The premise of using an electromagnetic flowmeter is that the liquid to be measured must be electrically conductive, and the conductivity below the threshold will lead to measurement errors that cannot be used until the threshold is exceeded, even if the change can be measured, indicating that the error varies little. The conductivity of industrial water and its aqueous solution is greater than 10-4S/cm, and the conductivity of acid, alkali and salt solution is between 10-4 and 10-1S/cm. There is no problem in using, and the low degree distilled water is 10-5S/cm, and there is no problem. Usually, the conductivity of sewage is high, because it contains more ions, which is one of the advantages of electromagnetic flowmeter for measuring sewage, which is determined by its principle of measurement.
In addition, some characteristics of the electromagnetic flowmeter also determine that it is more suitable for sewage measurement than other flow meter products. The electromagnetic flowmeter is not affected by temperature, pressure, viscosity and other external factors, the measuring tube caused by the pressure loss, no internal contraction or bulge in the initial signal detected by flow elements, is a precise linear change of voltage and average velocity of fluid, it has nothing to do with the other properties of fluid, has the superiority great. According to the sewage with large flow changes, impurities, corrosion, and a certain conductivity and other characteristics, to measure the flow of sewage, electromagnetic flowmeter can be said to be the best choice.
The electromagnetic flowmeter has the advantages of compact structure, small size, convenient installation, operation and maintenance. The measuring system adopts intelligent design, the whole seal is strengthened, and it can work normally in bad environment. Compared to other flow meter products, vortex flowmeter due to technical reasons, caliber is difficult to make big, quality, pipe type ultrasonic flowmeter in price relative to electromagnetic, lack of competitive advantage. So in the water supply and drainage and sewage treatment industry, electromagnetic flowmeter, especially large diameter electromagnetic flowmeter has great advantages, and has been very common application.
Sewage treatment process mainly through biological oxidation, flocculation, sedimentation and other processes to achieve the purpose of sewage purification, each stage requires a certain flow meter to measure. In the sewage treatment process, according to the process requirements, configuration of the corresponding detection instrument, constitute a reliable control system.
General sewage treatment plants need to be equipped with a flow meter in the following process test procedure:
(1) inlet pipe;
(2) test of mud from primary settling tank to storage tank;
(3) sludge and sludge flow measurement in sludge pumping station;
(4) sludge flow measurement in sludge pumping station;
(5) the discharge volume test of the two sedimentation tank distribution well;
(6) detecting the amount of mud in the digester;
(7) test of mud output in digestion tank;
(8) flocculation tank, dose detection, etc..
Therefore, the sewage treatment is inseparable from the electromagnetic flowmeter. With the increasing emphasis on environmental protection, the electromagnetic flowmeter used in sewage treatment will also usher in an unprecedented prosperity market.
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