Application of electromagnetic flowmeter in underdrain pumping station

Case introduction

Flow measurement is one of the basic tasks of water conservancy projects. In water diversion projects, the accuracy of flow measurement is directly related to The economic benefits and development prospects of production management units are very important.

1. The concept of flow meter

A flow meter is an instrument used to measure the volume of liquid or gaseous substances. In the early 1950s, flow meters achieved industrial application; 70 It has been widely used in various industries; its instrument performance has been greatly improved in recent years and it is widely used in various industries. An electromagnetic flowmeter is an instrument that measures the volume flow of conductive liquids based on Faraday's law of electromagnetic induction. In the early 1950s, electromagnetic flow meters realized industrial application; after the 1970s, the keyed low-frequency rectangular wave excitation method appeared, gradually replacing the early application of power frequency AC excitation method, and the performance of the instrument was greatly improved, and it was More widely used; in recent years, the output of electromagnetic flowmeters has gradually accounted for 5%-6.5% of the number of industrial flow meters.

2 Points of electromagnetic flowmeters

Electromagnetic flowmeters The advantages of the flow meter are: it is not affected by changes in temperature, pressure, density, drilling degree and conductivity (not less than z-low conductivity); the sensor has a simple structure, no throttling parts, and no clogging, so it is suitable for applications with solid particles , measurement of fibers and floating objects; simple installation, no need to cut off the flow, and holes can be opened on site under pressure; zero-point self-calibration eliminates zero offset, and the range can be set arbitrarily within the maximum calibrated flow range; forward and reverse flow measurement, If there are no special requirements, the factory setting is forward measurement; the instrument coefficient can be modified for different conductive media. The disadvantages of electromagnetic flowmeters are: they are relatively expensive, difficult to calibrate, and the overall structure is complex.

3 Application scope of flow meters

Flow meters can generally be used in water, ship hull operation and maintenance, water supply and drainage, energy-saving monitoring systems, water-saving management, power plants, papermaking and manufacturing Slurry, heating and heating, leakage detection, metallurgy, mining, flow inspection, flow tracking and collection, petroleum, chemical industry, heat measurement, heat balance, food and medicine, flow, thermal management, monitoring network system, etc. The Erzhuang culvert pumping station is mainly used for specific applications in water transmission pipelines or water transmission channels.

4 Basic principles of electromagnetic flowmeter

The working principle of electromagnetic flowmeter is Faraday’s law of electromagnetic induction. The flowmeter measuring tube is a non-magnetic alloy tube lined with edge material. The two electrodes are installed perpendicular to the axial flow direction, and the electrode head is flush with the surface of the inner tube. When the excitation coil is excited by square wave pulses in both directions, a magnetic field with a magnetic flux density of day is generated.

5 Maintenance of the electromagnetic flowmeter

The flowmeter should undergo key maintenance once a year. In order to maintain the transducer, the key maintenance time should be arranged during the unit or pipeline overhaul or outage time. For fee meterFor flowmeters with a certain amount of flow, the metering method during maintenance and outage should be negotiated with the user before carrying out key maintenance. Since the host of the flow meter needs to be inspected and repaired during regular key maintenance, the original operating data may be lost. Therefore, before the equipment is shut down, the operator should record the flow, cumulative flow and various operating status values. If the originally set parameter values ​​are not archived, they should all be recorded before the flowmeter is shut down for reference when it is put into operation again.

The thermal relay action is not reset, and the thermal relay is reset. If the cooling equipment is *, it should be able to be restarted.

5. 1. Host maintenance items

First use a vacuum cleaner to clean the inside and outside of the flow meter host. For the flow rate put into operation during the construction period, Because there is too much dust, the electronic plug-in board and connectors should be cleaned with * after vacuuming. Check all plug-in boards of the flow meter to see if the plug connectors are loose. If so, tighten them. Secondly, use a multimeter to check that the input AC power supply and voltage value should be within the specified range. Finally, check the waveform and amplitude of the received signal. This check must be performed under the conditions that the pipe under test is filled with water and the transducers of all sound paths are correctly connected to the host. Enter the submenu "Debug Diagnosis" menu under the "Utilities" menu of the flow meter and check whether all the sound channel signals are normal. If there are any abnormalities, they can be eliminated through debugging and diagnosis.

5.2 Key maintenance of the transducer and signal cable

First check whether the exposed parts of the transducer and signal cable are damaged, loose or leaking. Check the resistance of the transducer and cable, remove the terminal of the back panel of the transducer signal cable expansion box, and use a 500V megohmmeter to check the resistance of each transducer and cable from the cable end connector. The insulating resistance of the cable assembly should not be less than 20MQ. For transducers and cables whose insulating resistance does not meet the requirements, the reasons must be identified and dealt with. Inspect the built-in transducer into the pipe. When the pipeline under test is out of service, send people into the pipeline to inspect the built-in transducer tube. The inspection contents include: Check whether there are aquatic organisms or water creatures on the emission surface of the built-in transducer tube. Limescale has accumulated and should be removed if present. Check whether the fastening screw of the built-in transducer is loose. If it is loose, tighten it and calibrate it with a laser cat sight. Check whether the cable protective tube is broken, loose or corroded, and if so, handle it accordingly. For open channel flow meters, pay attention to checking the working condition of the water level transducer. There should not be any debris in the water level well. If there is mud on the surface of the transducer, it should be cleaned in time.

5.3 Re-operation after key maintenance

After the flow meter has undergone key maintenance, the following work should be done before it is put back into operation: Check the input and output voltage of the power supply All meet the specified requirements; check that all parameters are correct; enter the "Debugging Tools" menu of the flow meter to perform a self-test on the host and debug each sound path to see if the various signals are normal. Check the flow meterShows whether the instrument is normal.

6 Conclusion

In summary, electromagnetic flowmeters are widely used in pump stations, integrating many advantages, such as simple installation and accurate measurement. , during the operation of the underdrain pumping station, the equipment operates stably and the measurements are relatively accurate, ensuring safe water delivery from all aspects.