Industry new

Description of application technology of electromagnetic flowmeter in water supply system

With the continuous development of China's water supply industry, it is required to provide more accurate flow metering for water supply and distribution, and it is also an important means to improve the economic benefits of water supply enterprises. The application of electromagnetic flowmeter in water supply system is more and more extensive, and has nothing to do with conductivity, pressure and temperature, and is not affected by these parameters, and the accuracy and reliability of measurement are high. The electromagnetic flowmeter needs to combine computer information technology to collect, convert, analyze and then accurately simulate the signal to analyze the flow change. The advantage is that the operation is simple, the accuracy is high, and the process of manual identification is reduced.

1
The basic principle of electromagnetic flowmeter

The electromagnetic flowmeter is based on the law of electromagnetic induction. When the fluid is used as a conductor, when the magnetic field lines are passed, the magnetic field is cut, and the electromotive force induced electromotive force E=K×V×B×D is generated, where E refers to the induced electromotive force, and K is Instrument constant, V is the average flow rate, B refers to the magnetic induction, and D is the inner diameter of the measuring tube. The fluid flows perpendicular to the direction of the magnetic field, and the induced electromotive force is positively correlated with the unit volume voltage or the average flow rate. The signal of the induced voltage is measured and processed by the amplifier to be converted into a uniform output signal.

2
Application Research of Electromagnetic Flowmeter in Water Supply System

❖ 2.1 Main technical features and installation requirements of electromagnetic flowmeter

2.1.1 Main technical characteristics of electromagnetic flowmeter

The technical characteristics of the electromagnetic flowmeter mainly include five aspects. First, there is no obstruction in the measuring tube, the pressure loss is small, and the interference of the water supply flow measurement is small. Second, since the measurement results are not affected by certain factors, such as temperature, pressure, etc., this ensures high accuracy and stability. Third, only the electrodes and pipes are in contact with the liquid to be tested, so the influence on the electrodes is not large. Only the selection of reasonable wear-resistant and corrosion-resistant materials can ensure the reliability of the electrode operation. Fourth, the flow in the forward and reverse directions can be measured. Fifth, the way of outputting signals is very flexible, and can be specifically selected according to the characteristics of the working environment, such as current, frequency, pulse, and the like.

2.1.2 Requirements and installation requirements for electromagnetic flowmeters

The use and installation of electromagnetic flowmeters are required to meet strict requirements. Generally, it is necessary to start from four aspects. The first is to have clear regulations for upstream and downstream pipelines: for straight pipelines with an upstream length of more than 5 pipe diameters, the downstream is more than 3 times. The straight pipe length of the pipe diameter should increase the length of the upstream and downstream pipes when encountering a special working environment. Second, the grounding resistance should be strictly controlled, generally below 10O ohms. Third, it is necessary to avoid interference from external electromagnetic waves to the electromagnetic flowmeter. Fourth, install valves in the upstream pipeline, especially in locations that seriously affect the flow characteristics, such as right angle bends and butterfly valves, it is best to install a rectifier to stabilize the flow of water and accurately meter.

❖ 2.2 Online calibration of electromagnetic flowmeter

The electromagnetic flowmeter has been verified at the manufacturer before purchase, but the environment of the water supply system is complex and there are various factors, so the production environment and the use environment are very different. Once put into the field, the components of the electromagnetic flowmeter are affected by many factors, and there may be failures. The routine field calibration is required before the first use, but the electromagnetic flowmeter is installed in the water supply pipeline, which is difficult to disassemble. Online verification. The online verification mainly includes five aspects. First, the excitation coil is tested for copper resistance. In the case of the same ambient temperature, the resistance value is consistent with the original factory value. Second, the safety insulation of the excitation coil is tested, and the insulation resistance value must exceed 20 megaohms. Third, the resistance of the sensor electrode to the ground is tested. If the resistance value is between 2-20kv, it needs to be tested several times to take a stable test value. When the charge and discharge phenomenon occurs, and the resistance value of the two poles is close, it is qualified. Fourth, when testing the converter excitation current, the original current value and output value of the converter should be observed. When the error is less than 0.25 mA, it is qualified. Fifth, test the converter analog output and frequency output, when the maximum linearity error is less than 0.5%, it is qualified.

❖ 2.3 Application of electromagnetic flowmeter in water supply system

2.3.1 For regional metering

The application of electromagnetic flowmeters in urban pipe networks is quite common, especially for the metering and distribution of water supply, which facilitates the scheduling and configuration of water. Taking a water supply situation in an urban area as an example, some pipelines are DN600 and DN800. The new pipe has a large flow rate and the leakage is not serious. Therefore, it is necessary to select an electromagnetic flowmeter with high sensitivity and a wide measurement range.

2.3.2 Use as a settlement meter

An important purpose of water supply flow metering is water meter settlement. Electromagnetic flowmeters are used as settlement water meters and have important reference functions. The flowmeter management program is to analyze the requirements of the electromagnetic flowmeter, such as model, quantity, etc., and then purchase, archive, install, use, check, etc., and require regular maintenance.

2.3.3 For water metering of water plants

Electromagnetic flowmeters are widely used in current water plants, laying a sufficient foundation for water allocation and scheduling, providing data reference for production management, facilitating chlorine and water purification, etc., so that chlorine consumption and drug consumption can be accurately calculated. Data such as power consumption, convenient for cost control and water treatment. The water supply system will also have a certain degree of failure, and the abnormality will result in inaccurate measurement. The electromagnetic flowmeter can respond to the abnormality of the unit or the bursting of the water supply pipeline in time. The electromagnetic flowmeter provides reference for the dispatching of the urban pipe network, and the long water pressure and the flowmeter work together to provide data reference for the operation of the unit. The stability of the electromagnetic flowmeter is good, and the measurement accuracy is high. However, an imported ultrasonic flowmeter of the same precision level is required for checking, and the time for checking is set, so that the error can be better controlled.

❖ 2.4 Difficulties and solutions in the use of electromagnetic flowmeters

The environment used by the water supply system is relatively complicated, and the electromagnetic flowmeter is required to have high stability and reliability. However, there are various problems and difficulties in actual use. The following is a brief analysis.

(1) The installation conditions of the flowmeter are not satisfied. The installation of the electromagnetic flowmeter has high requirements for the straight pipe section, but it is difficult to install in the old water supply system, which will affect the stability of the measurement. The flow characteristics can be improved by adding a rectifier tube.

(2) The flow rate of the water to be measured is too low. The flow rate of the water flow is proportional to the induced electromotive force, but if the flow rate of the water flow is too low, it will affect the accuracy of the measurement, especially at the end of the pipe network. The corresponding method is to open the valves on both sides of the boundary as much as possible.

(3) The surface of the sensor should be clean and there should be no sludge. If there is sludge, the measurement will be accurate due to the conductivity of the sludge. When selecting the electrode, the blade type electrode can be used, and the maintenance plan is made to reduce the interference factor of the electrode, ensure the stability of the electrode and ensure its normal operation.

(4) If there is moisture in the pipeline, it will disturb the normal measurement and affect the accuracy of the measured value. When water vapor is present in the pipeline, it is necessary to find the cause and handle it accordingly. If necessary, an exhaust valve can be installed to remove the water vapor.

(5) The inlet pipe of the electromagnetic flowmeter should be kept unobstructed, and there should be no deposits. Otherwise, it will affect the flow characteristics of the electromagnetic flowmeter, affect the accuracy of the measurement, and cause measurement errors, so it needs to be cleaned up in time.

(6) Lightning damage The electromagnetic flowmeter is a common accident, and slight will also affect the accuracy of its work, such as signal interference. Especially in the relatively empty suburbs, the area covered by thunderstorms will have a great impact on the electromagnetic flowmeter, and it is necessary to install corresponding lightning protection devices. When dealing with such problems, you need to do power protection, grounding protection and so on. The work of lightning protection and lightning protection is very important. Usually, the grounding grid, the installation of lightning rods, and the construction of houses on the electromagnetic flowmeter well can obviously improve the lightning protection and lightning protection capability of the electromagnetic flowmeter. If such problems cannot be solved fundamentally, separation protection is required and losses can be reduced.

PREVIOUS：Advantages of electromagnetic flowmeter compaNEXT：Electromagnetic flowmeter strengths and defec