A Brief Analysis of the Application of Electromagnetic Flow Meters

Flow is a commonly used process control parameter in industrial production and an important production technical indicator in the water supply industry. The accuracy of flow measurement will affect the correct calculation and reliability of important indicators such as cost accounting and energy consumption for enterprises. Therefore, it is crucial to choose high-quality, stable, and accurate flow measuring instruments.

With the development of science and technology, new types of flow measuring instruments are constantly emerging, with a wide variety and different performances, and their usage conditions and technical parameters also vary. For users, it is essential to first understand the performance characteristics of flow measuring instruments and combine them with the specific working conditions of their unit to make the correct choice.

Our company has used various types of flow measuring instruments over the years, such as turbine flow meters, ultrasonic flow meters, insertion-type and measuring tube electromagnetic flow meters, including both domestic and imported instruments, each with different working performances and usage effects.

In order to achieve relatively accurate measurement of water supply, our company has invested significant funds in recent years to update and transform the existing flow measuring instruments. In the early selection process, we carefully analyzed, compared, and verified the actual application situations, existing problems, installation difficulties, and performance-to-price ratios of various flow measuring instruments used in the past. We believe that electromagnetic flow meters have advantages such as sensitive response, good linearity, high accuracy, and are not affected by factors such as the temperature and viscosity of the measured medium during measurement. Although installation is relatively complex, we adopted new installation techniques for flow meters installed on cast iron pipelines, reducing installation difficulty and minimizing water outage time. Therefore, in the selection of flow measuring instruments, we mainly chose electromagnetic flow meters produced by Kaifeng Instrument Factory. Through years of practical application, we have realized that to ensure the safe and stable operation of the instruments, it is necessary to create good on-site conditions and strictly follow technical requirements for correct installation and debugging, implementing centralized management to ensure the normal operation of flow meters and achieve continuous and accurate measurement. Below are the specific practices of our company in the application of electromagnetic flow meters (taking the E-mag electromagnetic flow meter from Kaifeng Instrument Factory as an example) for discussion.

1. Selection of Instrument Well Location

The location of the instrument well should meet the requirements of the flow meter for the straight pipe sections before and after it, that is, the length of the upstream straight pipe section should be greater than 5D (D is the pipe diameter), and the downstream straight pipe section should be greater than 2D, to ensure symmetrical distribution of flow velocity and eliminate measurement errors caused by this.

The installation location should avoid strong vibrations, stay away from strong interference sources, and ensure that the pipeline is filled with water.

2. Correct Installation of the Instrument

1. Installation of the Sensor

The installation of the electromagnetic flow meter is divided into the installation of the sensor and the installation of the converter. Especially for the installation of the sensor, it requires stopping water, cutting pipes, pumping water, welding, or punching, making the installation work quite difficult and requiring a long time for water stoppage, resulting in certain economic losses. In response to this situation, when installing flow meters on cast iron pipelines, we adopted new technological methods, using two single-disc compensators to replace the traditional short pipes A and B, eliminating the punching process and the maintenance time for the pipe ends. Particularly in cases where the valve does not close tightly, it can be operated with water. After stopping the water, installing a sensor only takes half a day to restore water supply, thus shortening the installation time and reducing economic losses caused by water stoppage, while also achieving certain social benefits.

2. Proper grounding of the sensor housing is a necessary condition to ensure the normal and stable measurement of the flow meter.

It is generally believed that the sensor is installed on a metal pipeline, and since the pipeline is buried underground and the line is very long, it itself serves as a large grounding electrode, and the instrument does not need further grounding treatment. However, two issues are overlooked: one is that the pipeline is generally treated for corrosion prevention, and the second is that the connection flange and pipeline are separated by punching or rubber pads, which greatly increases the grounding resistance of the sensor, affecting the normal operation of the flow meter.

In our practical application, we once had a flow meter that did not work properly after being put into use, with flow display sometimes present and sometimes absent, even triggering an empty pipe alarm. At that time, we could not find the cause based on the fault phenomenon. Later, we provided a separate grounding electrode for the sensor, and the fault phenomenon immediately disappeared, and it has been operating normally ever since.

Therefore, after the flow meter is installed, the grounding resistance should be measured. If the resistance value is too high, it is best to create a grounding electrode to reduce interference potential caused by stray currents.

3. Usage Situation

After several years of actual operation and observation comparison, we believe that the operational situation of the electromagnetic flow meter in our company's production is superior to that of other instruments previously used.

1. The electromagnetic flow meter has high accuracy, good linearity, and stable operation, improving the accuracy of measurement and the reliability of data, overcoming the issue of some instruments being unstable in operation, which led to unreliable measurement data. After multiple on-site comparisons, the errors were all within the controlled range, enhancing trust in the instruments, ending the unscientific measurement method of calculating water volume based on the performance curve of the pump, and effectively ensuring that data collected by the instruments is the standard, avoiding human factors.

2. The electromagnetic flow meter has a simple structure, with no moving parts in the sensor, eliminating measurement errors or instrument failures caused by mechanical wear or entanglement of impurities, resulting in a very low failure rate and significantly reduced maintenance, thus saving a lot of human and material resources.

Since 1992, our company has installed and used 18 electromagnetic flow meters produced by Kaifeng Instrument Factory. Up to now, only one converter has failed due to a relatively humid installation location, while the other instruments are functioning normally.

3. The electromagnetic flow meter has various interface circuits, allowing for easy connection with data collection terminals or computers, achieving automation of data collection, analysis, and management. All of our flow meters are connected to the dispatch system of the headquarters, and the original data of water supply and source water volume have entered the computer collection and transmission network, greatly improving the authenticity and fairness of measurement detection data, laying a solid foundation for the scientific and standardized measurement detection.

4. Management of Flow Meters

Our headquarters has a relatively large number of installed flow meters, with installation locations dispersed. The source water volume and supply volume of all factories under the headquarters are basically calculated according to the flow meters. To facilitate management, the Measurement and Testing Center of the headquarters is responsible for the maintenance, debugging, and verification of all flow meters, conducting unified management.

1. Establish a running file for flow meters, including the manufacturer, model, production date, installation location, pipe diameter, calibration time, etc., to facilitate the maintenance and management of the instruments.

2. Strengthen inspection and checking work, and conduct regular testing and calibration. We mainly use two methods: first, measuring and comparing with a relatively high-precision portable flowmeter and an electromagnetic flowmeter; second, using a flow instrument calibrator to verify the flow converter, checking whether various technical indicators are correct, and archiving the test data.

3. Compare the test data with previous test results, carefully analyze and study any suspicious data that appears, investigate possible causes, address and resolve them in a timely manner, and produce an analysis report on the operation of the flowmeter.

The above is our superficial understanding, for reference only.