Common fault analysis of electromagnetic flowmeter
1. Failure during debugging
Debugging expectation failure generally occurs in the stage of instrument installation and debugging. Once eliminated, it will not occur again under the same conditions in the future. Common commissioning failures are usually caused by improper installation, environmental disturbances, and fluid characteristics.
1) Installation
Usually, the fault is caused by the incorrect installation position of the electromagnetic flow sensor. For example, if the sensor is installed at the highest point of the piping system where gas is easy to accumulate; Back pressure, the fluid is directly discharged into the atmosphere to form a non-full tube in the measuring tube.
2) Environmental aspects
Usually, it is mainly caused by pipeline stray current interference, strong electromagnetic wave interference in space, magnetic field interference of large motors, etc. Pipeline stray current interference usually takes good separate grounding protection to obtain satisfactory results, but if encounter strong stray current (such as electrolysis workshop pipeline, sometimes the AC potential peak Vpp induced on the two electrodes can be as high as 1V), still Additional measures and flow sensor and pipeline insulation are required. Space electromagnetic wave interference is generally introduced through signal cables, which are usually protected by single-layer or multi-layer shielding.
3) Fluid aspect
The evenly distributed tiny air bubbles in the measured liquid usually do not affect the normal operation of the electromagnetic flowmeter, but as the air bubbles increase, the
The output signal of the meter will fluctuate. If the bubbles are large enough to cover the entire electrode surface, the electrode circuit will be instantaneously disconnected as the bubbles flow through the electrode, resulting in greater fluctuations in the output signal.
When the electromagnetic flowmeter with low frequency square wave excitation measures the slurry with too much solid content, it will also generate slurry noise, which will cause the output signal to fluctuate.
When measuring mixed media, if the flow sensor is measured before the mixing is uniform, the output signal will also fluctuate.
Improper selection of electrode material and measured medium will also affect normal measurement due to chemical action or polarization. The electrode material should be correctly selected according to the instrument selection or related manuals.
2. Runtime failure
The fault during operation is the fault that occurs after the electromagnetic flowmeter has been debugged and operated normally for a period of time. Common faults during operation are generally caused by factors such as the adhesion layer on the inner wall of the flow sensor, lightning strikes, and changes in environmental conditions.
1) Sensor inner wall adhesion layer
Because electromagnetic flowmeters are often used to measure dirty fluids, after a period of operation, adhesion layers often accumulate on the inner wall of the sensor and cause failures. These failures are often caused by the electrical conductivity of the adhesion layer being too large or too small. If the adhesion layer is an insulating layer, the electrode circuit will be open and the meter will not work normally; if the conductivity of the adhesion layer is significantly higher than that of the fluid, the electrode circuit will be short-circuited.
The meter also doesn't work properly. Therefore, the attached scale layer in the measuring tube of the electromagnetic flowmeter should be removed in time.
2) Lightning strike
Lightning strikes easily induce high voltage and surge current in the instrument circuit, which damages the instrument. It is mainly introduced through the power line or the excitation coil or the flow signal line between the sensor and the converter, especially from the control room power line, which accounts for most of it.
3) Changes in environmental conditions
During commissioning, since the environmental conditions are still good (for example, there is no interference source), the flowmeter works normally, and the installation conditions are often neglected at this time (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 flowmeter, installing a large transformer nearby, etc.), it will interfere with the normal operation of the meter, and the output of the flowmeter will The signal will fluctuate.