Electromagnetic flowmeter for sewage measurement

Introduction to sewage treatment: sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production sewage includes industrial sewage, agricultural sewage and medical sewage, etc., and domestic sewage is sewage produced by daily life. It refers to a complex mixture of various forms of inorganic and organic materials, including: 1 floating and suspended solid particles; 2 glue Shape and gel-like diffuser; 3 pure solution. According to the nature of water pollution, there are two types of water pollution: one is natural pollution; the other is artificial pollution. At present, the most harmful to the water body is man-made pollution. Water pollution can be divided into chemical pollution, physical pollution and biological pollution according to different pollution impurities. The main pollutants are: (1) industrial wastewater discharged without treatment; (2) domestic sewage discharged without treatment; (3) farmland sewage using a large amount of chemical fertilizers, pesticides and herbicides; (4) stacked in the river Industrial waste and domestic garbage; (5) soil erosion; (6) mine sewage.

What substances are contained in industrial wastewater? The chemical properties of major pollutants contained in industrial wastewater are classified into: inorganic wastewater containing inorganic pollutants, organic wastewater mainly composed of organic pollutants, mixed wastewater containing both organic and inorganic materials, heavy metal wastewater, and radioactive content. Waste water of matter and cooling water contaminated only by heat. For example, wastewater from electroplating wastewater and mineral processing is inorganic wastewater. Wastewater from food or petroleum processing is organic wastewater. In the printing and dyeing industry, mixed wastewater is used in the production process. Different industries exclude different wastewater components.

Application of electromagnetic flowmeter in sewage measurement: At present, in the measurement of sewage of major enterprises, the sewage flowmeter used for pipeline sewage measurement widely uses electromagnetic flowmeter, and the open channel sewage metering uses ultrasonic open channel flowmeter. Electromagnetic flowmeters are widely used in various industries such as water/wastewater, chemical, pharmaceutical, paper, and food. Large-diameter instruments are mostly used in water supply and drainage projects. Medium and small calibers are often used in solid-liquid double equal unpredictable fluids or in high-demand locations. Small caliber and small caliber are often used in places with hygienic requirements such as the pharmaceutical industry, food industry, and bioengineering. With the acceleration of China's industrialization process, the problem of environmental pollution is becoming more and more serious, and the voice of society for sustainable development is getting higher and higher. The concept of harmonious coexistence between man and nature is accepted by people, and the treatment of various pollution is more urgent.

What should I consider when choosing an electromagnetic flowmeter for wastewater measurement? The electromagnetic flowmeter is first considered when designing the design institute and the user engineer. Only when the smart electromagnetic flowmeter cannot be used for its measurement medium will other types of flowmeters be considered. Everyone knows that it is the best flow meter for measuring liquid media. As long as the selection is correct and the installation is correct, it can play an accurate measurement. As long as it pays attention to product maintenance, it can work for a long time. It is widely used because of its high measurement accuracy, low failure, easy installation, long service life, high safety, multiple functions, intuitive display and simple setup. As an instrument manufacturer, we are striving to develop more accurate and more functional flowmeter products to meet the different needs of different users.

What are the components of the electromagnetic flowmeter? It consists of two parts: flow sensor and transmitter. The excitation measuring coil is arranged on the upper and lower sides of the measuring tube. After the excitation current flows, 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 transmitter. The field current is provided by the transmitter. According to the converter and sensor assembly method, there are two types: separate type and integrated type. In the sewage treatment process, large-diameter flowmeters are mostly split type, one part is installed underground and the other part is on the ground. The small caliber is more integrated. The working principle of the electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. When the conductive metal rod moves at a certain speed perpendicular to the direction of the magnetic line, an induced voltage is generated. If the magnetic field strength is B, the length of the metal rod is L, and the speed is v, then the induced voltage is 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 Produces a constant magnetic field. When a conductive medium flows, an induced voltage is generated. The two electrodes inside the pipe measure the induced voltage generated. The measuring tube is electromagnetically isolated from the fluid and the measuring electrode by a non-conductive inner liner (rubber, Teflon, etc.).

Differences in the quality of electromagnetic flowmeters: The functions of electromagnetic flowmeters on the market are also very different. The simple ones are only measuring one-way flow, only outputting analog signals to drive the rear position meter; multi-function meters have two-way flow, range switching, upper and lower limit flow Alarm, air traffic control and power cut off alarm, small signal cutoff, flow display and total calculation, automatic check and fault self-diagnosis, communication with host computer and motion configuration. The serial digital communication function of some models can be selected from a variety of communication interfaces and dedicated chips (ASIC) to connect HART protocol system, PROFTBUS, Modbus, FF field bus and so on.

Why do you choose an electromagnetic flowmeter for measuring sewage? Electromagnetic flowmeters are found everywhere in industrial enterprises, and most of the pipes that measure liquid media use this flowmeter. Why the application is so extensive, because the measurement results and display methods and operation are simple to meet user requirements. User operators only need to learn how to use them through simple training. Will you choose the electromagnetic flowmeter? First of all, we must know which medium the meter can measure. Secondly, we must know the requirements of the meter for the flow range. Once again, we must know the requirements of the instrument for the installation conditions. Finally, we must know some factors that can affect the measurement accuracy.

What parameters do you need for electromagnetic flowmeters during the selection? The user should cooperate with the manufacturer to provide the following detailed parameters: 1. What is the liquid medium, whether the medium is corrosive, and the corrosive strength, which materials will corrode. In order for the manufacturer to determine the electrode and lining material of the smart electromagnetic flowmeter. 2. To know the maximum temperature of the medium, the working pressure is to further determine the lining material and determine the working pressure of the flange of the instrument. 3. Know the length of the straight pipe before and after the installation of the instrument and whether there is a valve before or after the bend to determine the instrument Whether the installation location can meet the measurement requirements. 3. Know how the instrumentation pipeline works and how the device behind the media works. If used in a natural flow location, the impact of this condition on measurement accuracy must be considered. 4. If the electromagnetic flowmeter is used for quantitative control, it should be taken seriously, what kind of regulating valve should be selected, and what kind of control instrument should be selected. Mainly consider the reliability and operability of the instrument. 5. To know the industrial site ambient temperature, instrument power supply selection, output information selection and communication mode selection. 6. When the user meter is used to quantitatively feed the equipment, the accuracy of the electromagnetic flowmeter is particularly important, and the quality of the product is thus apparent.

The electromagnetic flowmeter is introduced in the function: the aperture range of the electromagnetic flowmeter ranges from 6 mm to 2 m wide than other types of flowmeters. Accuracy can be 0.5%, 0.2% two options. The forward and reverse bidirectional flow can be measured, and the pulsating flow can also be measured. The premise of using an electromagnetic flowmeter is that the liquid to be tested must be electrically conductive and cannot fall below the threshold (ie the lower limit). If the conductivity is lower than the threshold, measurement error will be generated until it can not be used. If the threshold value exceeds the threshold, it can be measured even if the change is small. The threshold value of the general-purpose electromagnetic flowmeter is 10-4~(5×10-6)S/cm. Between, depending on the model. It also depends on the length of the flow signal line between the sensor and the converter and its distributed capacitance. The length of the signal line corresponding to the conductivity is usually specified in the manufacturer's instruction manual.

The conductivity of sewage water indicates that the conductivity of industrial water and its aqueous solution is greater than 10-4S/cm, and the conductivity of acid, alkali and salt liquid is between 10-4 and 10-1S/cm. There is no problem in use, low-grade distilled water. There is no problem with 10-5S/cm. Electromagnetic flowmeters cannot measure liquids with very low conductivity, such as petroleum products and organic solvents. It is not possible to measure gases, vapors and liquids containing more large bubbles. It is found from the data that some pure liquids or aqueous solutions have low conductivity and are considered to be unusable. However, in practice, examples can be used because they contain impurities, and such impurities are advantageous for increasing conductivity. For aqueous solutions, the conductivity in the data is measured in the laboratory using pure water ratio. The actual aqueous solution may be used in industrial water ratio, and the conductivity will be higher than that obtained, which is also beneficial for flow measurement.

Advantages of electromagnetic flowmeter: The electromagnetic flowmeter is not affected by external factors such as temperature, pressure, viscosity, etc., and there is no pressure loss caused by shrinkage or protruding part inside the measuring tube. In addition, the initial signal detected by the flow component is a The average flow velocity of the fluid is a precisely linear voltage that is independent of other properties of the fluid and has great advantages. According to the characteristics of large flow, large impurity, low corrosivity and certain conductivity, the electromagnetic flowmeter is a good choice for measuring the flow rate of sewage. It is compact and small in size. Easy to install, operate and maintain, the measuring system adopts intelligent design, the overall sealing is strengthened, and it can work normally in harsh environments. The vortex flowmeter is difficult to enlarge due to technical reasons. The quality and quality of the pipeline type ultrasonic flowmeter lack competitive advantage over the electromagnetic. Therefore, in the water and sewage industry, electromagnetic flowmeters, especially large-caliber electromagnetic flowmeters, have great advantages and have been widely used.

The electromagnetic flowmeter is available in IP67 (dust and water proof) or IP68 (dustproof and submersible). Large-caliber flowmeter sensors are mostly installed underground in wastewater plants, so IP68 (dust-proof and anti-submersible) is recommended. Generally, the electromagnetic flow has the following requirements for the installation field: 1) When measuring the mixed phase fluid, select the place that will not cause phase separation; when measuring the two-component liquid, avoid the downstream of the mixture that has not been uniformly mixed; when measuring the chemical reaction pipeline, Installed in the downstream of the fully completed reaction section; try to satisfy the straight pipe sections before and after the not less than 5D and 2D; 2) avoid the negative pressure in the measuring pipe as much as possible; 3) choose a place with small vibration, especially for the integrated instrument; 4) avoid There are large motors and large transformers nearby to avoid electromagnetic field interference; 5) It is easy to realize the place where the sensors are grounded separately; 6) Avoid high concentrations of corrosive gases in the surrounding environment as much as possible; 7) Avoid direct sunlight as much as possible