The common application of electromagnetic flowmeter in

    With the acceleration of China's industrialization process, environmental pollution problems are becoming increasingly serious, and the society's call for sustainable development is getting higher and higher. The concept of harmonious coexistence between man and nature is accepted by people, and the governance of various pollutions is more urgent. Shaoxing Water Treatment Development Co., Ltd. is an urban comprehensive sewage treatment enterprise mainly engaged in printing and dyeing industrial wastewater. The completed Phase I and Phase II projects have reached a sewage treatment capacity of 700,000 tons/day. Because in the sewage treatment process, it is necessary to measure and control the discharged sewage, additives, sludge, etc., so flow measurement is very important.
　　The electromagnetic flowmeter is not affected by external factors such as temperature, pressure, viscosity, etc. There is no pressure loss caused by contraction or protrusion inside the measuring tube. In addition, the initial signal detected by the flow element is a voltage that changes accurately linearly with the average flow velocity of the fluid. It has nothing to do with other properties of the fluid and has great advantages. According to the characteristics of sewage with large flow changes, impurities, low corrosiveness, and certain conductivity, the electromagnetic flowmeter is a good choice for measuring the flow of sewage. It has a compact structure and a small size. It is easy to install, operate and maintain. The measurement system adopts intelligent design and the overall sealing is strengthened, which can work normally in a harsh environment. However, due to technical reasons, it is difficult to make the vortex flowmeter larger in diameter and quality, and the pipeline ultrasonic flowmeter lacks competitive advantages in price compared to electromagnetic. Therefore, in the water and sewage industry, electromagnetic flowmeters, especially large-diameter electromagnetic flowmeters, have great advantages and have been widely used. The
　　E+HPROMAG series electromagnetic flowmeters are powerful and easy to operate. The specific features are as follows:
　　1. There are no obstructive flow parts in the measuring pipeline, no pressure loss, and the straight pipe section requires a low requirement.
　　2. The lining has a variety of materials such as hard rubber, polyurethane, PTFE, PFA, etc. to choose from.
　　3. The transmitter's DC power supply/AC power supply, four-wire/two-wire system, explosion-proof/non-explosion-proof, economical/standard type and other subdivisions meet your different needs.
　　4. The measurement is not affected by changes in fluid density, viscosity, pressure, temperature, and conductivity.
　　5. Photosensitive keys, can be operated without opening the cover; Chinese menu display, silicone rubber cable is more convenient for domestic users.
　　6. Quick setting menu, guide to complete parameter setting, convenient and fast.
　　7. High measurement reliability, good repeatability, and long-term maintenance-free. The range ratio is up to 1000:1
　　8. Various output modes such as current, frequency, pulse, Hart, profibus-PA, profibus-DP, FF are available for selection.
　　2. Measurement principle
　　The working principle of the electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When a conductive metal rod moves perpendicular to the direction of the magnetic field at a certain speed, an induced voltage will be generated.
　　In the electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in the Faraday test, and the two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When a conductive medium flows through, an induced voltage will be generated. The two electrodes inside the distribution isolator pipeline measure the induced voltage generated. The measuring pipeline is electromagnetically isolated from the fluid and the measuring electrode by non-conductive lining rubber, Teflon, etc.
　　Assuming that the magnetic field strength B generated by the electromagnetic induction coil is constant, the induced voltage Ue generated is proportional to the fluid velocity v, and the pipeline cross-sectional area A is known, the volume flow Qv can be calculated by the following formula:
　　The electromagnetic flowmeter consists of two major parts: a flow sensor and a transmitter. The sensor measuring tube is equipped with excitation coils above and below. After the excitation current is passed, a magnetic field is generated to pass through the measuring tube. A pair of electrodes are installed on the inner wall of the measuring tube in contact with the liquid, and the induced potential is drawn and sent to the transmitter. The excitation current is provided by the transmitter. According to the assembly method of the transmitter and the sensor, there are two types: separate type and integrated type. In the sewage treatment process, large-caliber flow meters are mostly split-type, one part is installed underground and the other part is on the ground. Small
　　-caliber flow meters are mostly integrated. The functions of electromagnetic flow meters on the market are also very different. The simple ones only measure unidirectional flow and only output analog signals to drive the rear instrument; multi-functional instruments have bidirectional flow measurement, range switching, upper and lower limit flow alarms, empty pipe and power cut-off alarms, small signal removal, flow display and total calculation, automatic verification and fault self-diagnosis, communication with the host computer and motion configuration, etc. The serial digital communication function of some models of instruments can select a variety of communication interfaces and dedicated chips ASIC to connect HART protocol systems, PROFTBUS, MODBUS, FF fieldbus, etc.
　　The caliber range of electromagnetic flowmeter is wider than other types of flowmeters. E+H provides three types of sensors: W, P, and H, which are used in water and sewage industry (W type), chemical and food industry (P type), and food and pharmaceutical industry (H type), with a caliber range from 2 mm to 2 m. The transmitter can provide multiple options of 10, 50, 23, and 53. 10 is an economical type developed for the water industry, 50 is a common type, 53 is an enhanced type, and 23 is a two-wire system. The accuracy can be selected from 0.5% and 0.2%. It can measure forward and reverse bidirectional flow, as well as pulsating flow.
　　The premise of using an electromagnetic flowmeter is that the measured liquid must be conductive and cannot be lower than the threshold, that is, the lower limit. If the conductivity is lower than the threshold, it will cause measurement errors until it cannot be used. If it exceeds the threshold, it can be measured even if it changes. The indication error of the bimetallic thermometer does not change much. The threshold of the general electromagnetic flowmeter is between 10-4 and 5×10-6S/cm, depending on the model. When used, it also depends on the length of the flow signal line between the sensor and the converter and its distributed capacitance. The manufacturer's instruction manual usually specifies the signal line length corresponding to the conductivity.
　　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 it. There is no problem with low-degree distilled water of 10-5S/cm. Electromagnetic flowmeters cannot measure liquids with very low conductivity, such as petroleum products and organic solvents. It cannot measure gases, steam, and liquids containing many large bubbles. From the data, it is found that some pure liquids or aqueous solutions have low conductivity and are considered unusable. However, in actual work, there will be examples that can be used because of impurities. Such impurities are beneficial to increase conductivity. For aqueous solutions, the conductivity in the data is measured in the laboratory with pure water ratio. The aqueous solution actually used may be proportioned with industrial water. The conductivity of Tiankang Instrument will be higher than that found, which is also beneficial to flow measurement.
　　In the sewage treatment process, it is necessary to configure corresponding detection instruments according to the process requirements to form a reliable control system. Shaoxing sewage treatment plant is equipped with flow meters in the following process detection procedures: 1 water inlet pipe; 2 mud volume detection from primary sedimentation tank to sludge storage tank; 3 sludge flow detection of residual and sewage integrated orifice flowmeter in sludge pump room; 4 sludge flow detection of return sludge in sludge pump room; 5 water flow detection of secondary sedimentation tank distribution well; 6 mud inlet detection of digester; 7 mud outlet detection of digester; 8 reagent inlet detection of flocculation tank, etc.