Why electromagnetic flowmeters are disturbed by magnetic fields

Mondo Technology Updated on 2024-01-31

Xiamen Hongkong Instrument Engineer will explain to you: why is the electromagnetic flowmeter disturbed by the magnetic field?

Electromagnetic flowmeter is a commonly used flow measurement instrument, and its working principle is based on Faraday's law of electromagnetic induction for flow measurement. During the measurement process, the electromagnetic flowmeter calculates the flow rate by measuring the induced potential generated by the perpendicular flow of a conductive liquid in a magnetic field. However, in practice, electromagnetic flowmeters can be affected by magnetic field disturbances, resulting in errors in measurement results. So, why do electromagnetic flowmeters be disturbed by magnetic fields?

First of all, we need to understand how electromagnetic flowmeters work. When a conductive liquid flows in a magnetic field, an induced electric potential is generated. The magnitude of this induced potential is directly proportional to the strength of the magnetic field, the effective length of the conductor in the magnetic field, and the relative velocity of the conductor in the magnetic field. Therefore, by measuring the magnitude of this induced potential, the flow rate of the conductive liquid can be calculated.

However, when other magnetic fields are present, they can interfere with the measurement of the electromagnetic flowmeter. This is because the magnetic field exerts a Lorentz force on the charges in the conductive liquid, changing its trajectory and thus affecting the measurement results. In addition, the magnetic field can cause eddy currents, which can affect the measurement of the induced potential, further leading to measurement errors.

Specifically, magnetic field interference mainly comes from the following aspects:

1.Earth's magnetic field: The earth itself is a large magnetic field. Although the Earth's magnetic field is relatively weak, the interference effect of the Earth's magnetic field on the electromagnetic flowmeter may gradually accumulate during long-term use, resulting in measurement errors.

2.Ambient magnetic field: Other magnetic fields present in the surrounding environment, such as current conductors, magnetic materials, etc., may also interfere with the electromagnetic flowmeter. In addition, if there are ferromagnetic substances in the pipes, it will also have an impact on the measurement of the electromagnetic flowmeter.

3.Electromagnetic field: The presence of an electric current or voltage produces an electromagnetic field. If there are cables, transformers and other equipment with high current or high voltage in the vicinity of the electromagnetic flowmeter, the electromagnetic field generated by it may interfere with the measurement of the electromagnetic flowmeter.

In order to reduce the impact of magnetic field interference on the electromagnetic flowmeter, the following measures can be taken:

1.Choose pipe materials with low magnetic field: In the selection of pipe materials, low magnetic materials, such as stainless steel, should be preferred to reduce the impact of magnetic field interference.

2.Optimize the installation position: Try to stay away from objects that may cause magnetic field interference, such as high-current, high-voltage equipment and magnetic materials. At the same time, try to avoid installing the electromagnetic flowmeter in areas that are susceptible to external environmental influences such as mechanical vibration and thermal radiation.

3.Use AC excitation measurement technology: AC excitation measurement technology reduces the effects of magnetic field interference by applying an AC excitation signal to a magnetic field coil. This technology can effectively improve the measurement accuracy and stability of electromagnetic flowmeters.

4.Calibration and compensation: The electromagnetic flowmeter is calibrated and compensated regularly to reduce the influence of magnetic field interference and other factors on the measurement results. Methods of calibration and compensation include the reference material method, the standard table method, the direct comparison method, etc.

In conclusion, electromagnetic flowmeters can be affected by magnetic field interference in practical applications, resulting in errors in measurement results. In order to reduce the impact of magnetic field interference on electromagnetic flowmeters, various measures can be taken, such as selecting piping materials with low magnetic fields, optimizing installation locations, using AC excitation measurement technology, and performing calibration and compensation. Through the application of these measures, the measurement accuracy and stability of the electromagnetic flowmeter can be effectively improved, and the accuracy of the measurement can be ensured.

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