Electromagnetic flowmeter commonly occurring failure analysis

If you find that the electromagnetic flowmeter is not working properly after it has been put into operation or has been put into normal operation for a period of time, you should first check the external conditions of the flowmeter, such as whether the power supply is good, whether the pipe is leaking or not full, and whether there are bubbles in the pipe. , whether the signal cable is damaged and whether the converter output signal (ie, the input circuit of the rear instrument) is open circuit. Remember to disassemble and repair the flow meter blindly.

Faults during the commissioning period

Faults during the commissioning period generally occur during the instrument installation and debugging stage. Once eliminated, they will not reoccur under the same conditions in the future. Common faults during commissioning are usually caused by improper installation, environmental interference, and fluid characteristics.

Environmental aspects

Usually mainly caused by stray current interference in pipelines, strong electromagnetic wave interference in space, magnetic field interference from large motors, etc. Pipeline stray current interference usually requires good independent grounding protection to obtain satisfactory results. However, if a strong stray current is encountered (such as electrolytic workshop pipelines, sometimes the AC potential peak value Vpp induced on the two electrodes can be as high as 1V), it is still possible to obtain satisfactory results. Additional measures need to be taken to insulate the flow sensor from the pipeline. Space electromagnetic wave interference is generally introduced through signal cables and is usually protected by single or multi-layer shielding.

Adhesion layer on the inner wall of the sensor

Since electromagnetic flowmeters are often used to measure dirty fluids, after running for a period of time, an adhesion layer will often accumulate on the inner wall of the sensor and cause failure. These failures are often caused by the conductivity of the adhesion layer being too large or too small. If the attachment is an insulating layer, the electrode circuit will be open-circuited and the instrument will not work properly; if the conductivity of the attachment layer is significantly higher than the conductivity of the fluid, the electrode circuit will be short-circuited and the instrument will not work properly. Therefore, the attached scaling layer in the electromagnetic flowmeter measuring tube should be removed in time.

In terms of fluids

The measured liquid contains evenly distributed tiny bubbles which usually do not affect the normal operation of the electromagnetic flowmeter. However, as the bubbles increase, the instrument output signal will fluctuate. , if the bubbles are large enough to cover the entire electrode surface, the electrode circuit will be instantly disconnected as the bubbles flow through the electrodes, causing greater fluctuations in the output signal. When an electromagnetic flowmeter with low-frequency square wave excitation measures slurry with excessive solid content, it will also produce slurry noise, causing the output signal to fluctuate. When measuring mixed media, if the flow sensor is entered for measurement before the mixture is uniform, the output signal will also fluctuate. Improper selection of electrode material and measured medium will also affect normal measurement due to chemical effects or polarization phenomena. The electrode material should be correctly selected according to the instrument selection or relevant manual.

Changes in environmental conditions

During the debugging period, the environmental conditions are still good (for example, there is no interference source) and the flow meter works normally. At this time, it is often easy to ignore the installation conditions (for example, the grounding is not very good). ). In this case, once the environmental conditions change and new interference sources appear during operation (such as electric welding on the pipeline near the flow meter, large transformers installed nearby, etc.), it will interfere with the normal operation of the meter and the output of the flow meter. The signal will fluctuate.