the common faults in the operation of electromagnetic flowmeter, some are due to instrument components damage caused by fault, some fault caused by improper selection, improper installation, environmental conditions, fluid properties and other factors, such as wave, instrument accuracy decreased or even damage etc.. it can generally be divided into two types: installation and commissioning of the fault (debugging period failure) and the normal operation of the fault (run-time failure).
(1) during the debugging period, the failure of debugging is expected to appear in the instrument installation and debugging phase. once it has been removed, it will not appear again under the same conditions. common debugging period failure is caused by improper installation, environmental interference and fluid characteristics.
1) installation is usually electromagnetic flow sensor installation location of the fault caused by incorrect, such as the highest point of common pipe sensor is installed in the easy accumulation of gas; or installed in a vertical pipe from top to bottom, there may be no pressure sensor after emptying; or, fluid directly into the atmosphere and the formation of the measuring tube in full pipe.
2) the environment is usually the pipeline stray current interference, strong electromagnetic interference in space, large motor magnetic field interference, etc.. pipeline stray current interference usually take good grounding protection alone can obtain satisfactory results, but if the stray current strong (such as electrolytic workshop pipeline, ac voltage peak vpp sometimes on the two electrode induction can be as high as 1v), still need to take additional measures and flow sensor and pipeline insulation etc.. space electromagnetic wave interference is usually introduced by signal cable, which is usually protected by single layer or multi-layer shielding.
3) the measured fluid containing tiny bubbles evenly distributed in the liquid usually does not affect the normal work of the electromagnetic flowmeter, but with the increase of air bubbles, meter output signals will fluctuate, if the bubble is large enough to cover the entire surface of the electrode, with the bubble flowing through the electrode electrode circuit makes the output signal and the opening moment more the fluctuation.
low frequency square wave excitation electromagnetic flowmeter to measure the excessive content of solid slurry, will also produce slurry noise, so that the output signal fluctuations.
when measuring the mixed medium, if the flow sensor is measured before the mixing is not uniform, the output signal will also fluctuate.
improper selection of electrode material and the measured medium will also affect the normal measurement due to the chemical action or polarization. the electrode material should be selected correctly according to the instrument selection or relevant manual.
(2) runtime fault fault is occurred during operation of electromagnetic flowmeter by debugging and normal operation after a period of time, the operation period of common faults in general by the flow sensor is attached on the inner wall layer, lightning strikes and the environment change caused by factors such as.
1) sensor attached on the inner wall of the electromagnetic flowmeter is often used to measure the layer due to dirty fluid, running after a period of time, often in the inner wall of the accumulation layer and sensor fault. these faults are often caused by too large or too small electrical conductivity of the adhesive layer. if the attachment is an insulating layer, the electrode circuit breaker will appear, the instrument is not working properly; if the attachment layer conductivity is significantly higher than the conductivity of the fluid, the electrode circuit will appear short, instrument can work normally. therefore, it is necessary to remove the fouling layer in the electromagnetic flowmeter.
2 lightning strikes lightning easily in the instrument circuit induced high voltage and surge current, so that the instrument damage. it is mainly through the power line or the excitation coil or the sensor and the converter between the flow signal lines and other ways, especially from the control room to introduce the majority of the power line.
3) environmental conditions during the commissioning period due to the environmental conditions are good (for example, no interference source), the flowmeter is working normally, at this time tend to neglect the installation conditions (such as grounding is not good). in this case, once the environmental conditions change, the emergence of new sources of interference during the operation (such as in the flowmeter for welding pipeline near, near the installation of large transformers), could interfere with the normal operation of the instrument, flow meter output signal will appear fluctuation.