With the acceleration of China's industrialization, the problem of environmental pollution has become increasingly serious, and the call of society for sustainable development has become increasingly high. The idea of harmonious coexistence between man and nature has been accepted by people, and the treatment of all kinds of pollution has become more urgent.Because in the sewage treatment process, it is necessary to measure and control the discharge of sewage, additives, sludge, etc., the flow measurement is very important.Among the many flow meters used for sewage measurement, electromagnetic flow meter is the absolute advantage, no matter from the principle point of view, or the accuracy of measurement, is the best.

Electromagnetic flowmeter is composed of flow sensor and transmitter.The sensor measuring tube is equipped with an excitation coil at the top and bottom. After the excitation current is passed, a magnetic field is generated through the measuring tube. A pair of electrodes are installed on the inner wall of the measuring tube and in contact with the liquid.The excitation current is supplied by the transmitter.According to the converter and sensor assembly classification, there are two types: separation type and one type.In the process of sewage treatment, the large-diameter flowmeter is usually divided, one part is installed underground, the other part is above ground.Small caliber is much with one - piece type.The working principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction.When the conductive metal rod moves perpendicular to the direction of the magnetic field line at a certain speed, the induced voltage will be generated.If the magnetic field intensity is B, the length of the metal rod is L, and the velocity is v, then the induced voltage is generated.

At present, the function of electromagnetic flowmeter on the market is also very different, the simple is to measure one-way flow, only output analog signal to drive the rear instrument;Intelligent electromagnetic flowmeter can measure two-way flow, range switching, upper and lower limit flow alarm, air pipe and power supply cut off alarm, small signal removal, flow display and total calculation, automatic check and fault self-diagnosis, communication with the upper computer and motion configuration.The serial digital communication function of some models of electromagnetic flowmeters can choose a variety of communication interfaces and special chips (ASIC) to connect HART protocol system, PROFTBUS, Modbus and FF fieldbus.

The premise of using the electromagnetic flowmeter is that the measured liquid must be conductive, and the measurement error will occur if the conductivity is lower than the threshold value until it cannot be used. Even if the threshold value is exceeded, the measurement error can be measured, and the error of the indicated value will not change much.The conductivity of industrial water and its aqueous solution is greater than 10-4S /cm, the conductivity of acid, alkali and salt solution is between 10-4 ~ 10-1S /cm, there is no problem with the use of low-degree distilled water is 10-5S /cm, there is no problem with the use of low-degree distilled water is 10-5S /cm.Usually sewage conductivity is high, because it contains many ions, which is one of the advantages of electromagnetic flowmeter used to measure sewage, determined by its measurement principle.

In addition, some characteristics of electromagnetic flowmeter also determine that compared with other flowmeter products, it is more suitable for sewage measurement.Electromagnetic flowmeter is not affected by the influence of external factors such as temperature, pressure, viscosity, measurements of the interior of the tube without shrinkage or bulge caused by the pressure loss, in addition, the flow element to detect the original signal, is an average flow velocity and fluid into precise linear change voltage, it has nothing to do with the other properties of the fluid, has the very big superiority.Then according to the sewage flow rate change, containing impurities, corrosion is small, has a certain conductivity and other characteristics, measurement of sewage flow, electromagnetic flowmeter can be said to be the best choice.

Still have the structure of electromagnetic flowmeter compact, volume is small, installation, operation, maintenance is very convenient, measurement system USES intelligent design, integral sealing is strengthened, can work normally under more adverse environment.Compared with other flowmeter products, vortex flow meter due to technical reasons, diameter is difficult to do large, quality, pipeline type ultrasonic flowmeter in price relative to electromagnetic lack of competitive advantage.So in the industry of water supply and drainage and sewage treatment, electromagnetic flowmeter especially large diameter electromagnetic flowmeter has great advantages, and has been widely used.

Sewage treatment process is mainly through biological oxidation, flocculation, precipitation and other processes to achieve the purpose of sewage purification, in each stage requires a certain flow meter to measure.In the sewage treatment process, the corresponding detection instruments should be configured according to the process requirements to form a reliable control system.

General sewage treatment plants need to be equipped with flow meters in the following process testing procedures:

(I)Intake pipes;

(2)Mud volume measurement from primary sedimentation tank to sludge storage tank;

(3)Sludge pump room residual, sludge flow detection;

(4)Sludge pump room reflux sludge flow detection;

(5)Detection of water flow rate of water distribution Wells in secondary sedimentation tanks;

(6)Detection of mud inflow into digester;

(7)Detection of mud output from digester;

(8)Flocculation pool agent intake detection and so on.

Therefore, sewage treatment is inseparable from the electromagnetic flowmeter. Along with the country pays more and more attention to environmental protection, the electromagnetic flowmeter used in sewage treatment will also usher in an unprecedented prosperous market.