Electromagnetic flowmeter is a widely used instrument, which plays an important role in the measurement of waste water and sewage. However, due to errors in model selection, installation and use, the accuracy of the final results may be affected, resulting in deviations in measurement data and even damage to the flowmeter. Why measurement errors in electromagnetic flowmeters may affect the accuracy of measurement results, and how to solve these problems.

1. The liquid to be tested contains bubbles.

This is a common phenomenon of bubbles in the liquid being tested. It is caused by external suction and internal liquid dissolution. However, the electromagnetic flowmeter cannot distinguish between liquid and air bubbles, so errors will be caused when calculating and measuring together. It is not recommended to install the electromagnetic flowmeter at the highest point of the pipeline, so it is easy to change the installation position. If the installation site is not easy to replace, please install an air collector upstream of the electromagnetic flowmeter and exhaust it regularly.

2. The tested liquid is not full in the pipeline.

Partially filled pipes are extreme cases with air bubbles. That is, the liquid in the pipe is not full, and a lot of bubbles are filled above the liquid in the pipe. If the liquid does not pass through the electrode, the measurement result will be greatly devalued, which is wrong in the engineering design. There are some requirements for the correct installation of electromagnetic flowmeters in different pipelines. Please keep this in mind, it will be helpful during installation to ensure the measurement accuracy of the electromagnetic flowmeter.

3. Short-circuit effect of conductive deposits

Due to the gradual deposition of conductive materials, the flow signal is short-circuited. This type of fault usually does not appear during debugging, but after a period of operation.

For the above problems, please disassemble the flowmeter and clean most of the brown rusted insulation layer, which is caused by a large amount of iron oxide precipitation in the electrolyte. You should analyze the possibility of such failures in any situation where the operation is normal at the beginning but the traffic is getting less and less over time.

4. The liquid crystallizes.

In the selection of electromagnetic flowmeters, we often encounter media that are easy to crystallize. Although most materials can be measured normally at room temperature, and the pipe has the function of heat dissipation and heat preservation in addition to the sensor measuring tube in the flowmeter, when ordinary fluid flows, the inner wall will be cooled to form a solid layer through the measuring tube. Therefore, please choose an electromagnetic flowmeter with a smaller measuring tube. It is not recommended to choose an electromagnetic flowmeter with too complicated installation requirements.

5. The conductivity of the liquid exceeds the allowable range.

The output impedance of the electrode depends on the conductivity of the liquid being measured and the electrode. When the conductivity is lower than the lower limit, the electromagnetic flowmeter will not work normally or the value display will slow down. In view of the above problems, the electromagnetic flowmeter can work normally after replacing the tantalum electrode normally.

6. Space electromagnetic interference

Generally, if the cable between the sensor and the converter is very long and there is strong electromagnetic interference around, the cable may introduce interference signals to form common mode interference, resulting in display distortion, nonlinearity or large-scale shaking. In response to this situation, first of all, please try to stay away from strong magnetic fields (such as nearby large motors, large transformers and power cables). Then, shorten the length of the cable as much as possible and take shielding measures.

7. Asymmetric flow of the measured fluid

Under normal circumstances, it is required that the current velocity of the fluid in the pipeline is axisymmetrically distributed and the magnetic field is uniform. In fact, there is usually a non-axisymmetric velocity distribution, and when a cyclotron current appears, it will affect the output, and then produce a larger measurement error. Therefore, some measures should be taken to avoid this situation. First, there are enough straight pipes upstream to ensure that the current velocity is distributed in concentric circles. In addition, the inner diameter of the electromagnetic flowmeter should be the same as the inner diameter of the pipeline within a certain range upstream and downstream, otherwise the current velocity distribution will be uneven. If there are not enough straight pipes upstream, a flow regulator can be installed, but this can only partially make up for it.

8. Vibration at the installation site will affect the accuracy of the electromagnetic flowmeter.

The electromagnetic flowmeter has strict requirements on the vibration of the installation site, so it must be installed in a place with less vibration, otherwise measurement errors will occur.