The ZH series electromagnetic flowmeter is powerful and easy to operate. The specific features are as follows: 1) Measure the unobstructed flow parts in the pipeline, no pressure loss, and the bottom of the straight pipe section.
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. A water treatment company in Zhejiang is an urban comprehensive sewage treatment enterprise mainly based on printing and dyeing industrial wastewater. The completed Phase I and Phase II projects have reached 700,000 tons/day of sewage treatment capacity. Because in the sewage treatment process, it is necessary to measure and control the discharge of sewage, additives, sludge, etc., so the flow measurement is very important.
1. Measurement principle The working principle of 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, 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, 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.).
Assuming that the electromagnetic induction coil produces a magnetic field strength (B) that is constant, the induced voltage (Ue) is proportional to the fluid velocity (v), and the cross-sectional area of ​​the pipe (A) is known, the volumetric flow rate (Qv) can be calculated by the following formula :
The electromagnetic flowmeter consists of two parts: the flow sensor and the 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 function of the electromagnetic flowmeter on the market is also very different. The simple one is to measure the one-way flow, and only output the analog signal to drive the rear position meter; the multi-function meter has the measurement bidirectional flow, range switching, upper and lower limit flow alarm, empty tube and power supply. 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.
The diameter of the electromagnetic flowmeter is wider than that of other types of flow meters. Jinhu Jinli Automation Instrument Co., Ltd. provides three types of sensors: W, P and H, which are used in the water and sewage industry (W type), chemical and food industries (P Type), food, pharmaceutical industry (H type), caliber ranging from 2 mm to 2 m. The transmitter can provide 10, 50, 23, 53 options, 10 for the economic development of the water industry, 50 for the common type, 53 for the enhanced type, 23 for the two-wire system. 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 industrial water and its aqueous solution is greater than 10-4 S/cm, and the conductivity of acid, alkali and salt liquid is between 10-4 and 10-1 S/cm. There is no problem in use, and low-grade distilled water is 10-5 S/ There is no problem with 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.
2. Characteristics of electromagnetic flowmeter The electromagnetic flowmeter is not affected by external factors such as temperature, pressure and viscosity. 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.
2) Measurement is not affected by changes in fluid density, viscosity, pressure, temperature, and conductivity.
3) The lining is available in a variety of materials such as hard rubber, polyurethane, PTFE, and PFA.
4) Transmitter DC power / AC power supply, four-wire / two-wire system, explosion-proof / non-explosion-proof, economic / standard type and other subdivision to meet your different needs.
5) Photosensitive keys can be opened without cover; Chinese menu display is more convenient for domestic users.
6) Quickly set the menu and guide the parameter setting, which is convenient and quick.
7) High reliability, good repeatability and long-term maintenance-free. Range ratio up to 1000:1
8) Provide various output modes such as current, frequency, pulse, Hart, Profibus-PA, Profibus-DP, FF, etc.
3. Installation requirements The ZH series electromagnetic flowmeters are available in IP67 (dust and water proof) or IP68 (dust and submersible). Large-caliber flowmeter sensors are mostly installed underground in wastewater plants, so IP68 (dust-proof and anti-submersible) is recommended. Usually electromagnetic flow has all of the following requirements for the installation site.
1) When measuring the mixed phase fluid, choose the place that will not cause phase separation; when measuring the two-component liquid, avoid the downstream of the mixing that has not been uniformly mixed; when measuring the chemical reaction pipeline, it should be installed downstream of the fully completed reaction section; Meet the straight pipe segments before and after: not less than 5D and 2D;
2) Avoid changing the inside of the measuring tube into negative pressure as much as possible;
3) Choose a place with small vibration, especially for integrated instruments;
4) Avoid large motors and large transformers nearby to avoid electromagnetic field interference;
5) It is easy to realize the place where the sensor is 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 4. Application and effect The sewage treatment process mainly achieves the purpose of sewage purification through biological oxidation, flocculation, sedimentation and other processes. At each stage, a certain amount of gauge is needed for measurement. In the miscellaneous sewage industry, Huai'an Zhonghang Instrument Co., Ltd. mainly provides 10W, 50/53W, 23W, 50/53P and other products.
Application of electromagnetic flowmeter in sewage treatment industry
Electromagnetic flowmeters have been used for more than 50 years and have been widely used in the world, covering water/wastewater, chemical, pharmaceutical, paper, food and other industries. 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.