Frequently encountered faults in the use of split electromagnetic flowmeters

Frequently encountered in the use of split electromagnetic flowmeters, the first is a common instrument failure, that is, the instrument structure or components cause damage failure; followed by external causes. Such as installation and flow distortion, deposition and scaling. The focus is on the causes of failure of the second category and applications.

According to the classification problem, it can be divided into: ( 1 ) operation failure; ( 2 ) debugging stage failure. The main reason for the failure of the debugging stage is the new and early stage of debugging. The main reason is that the selection or setup of the tool is unreasonable, the installation error is incorrect, and the main reason is that the fluid inclusions are attached to the electrode Li Ning, and the environmental changes are caused during operation. New sources of interference, etc.

According to the external source of the fault, it is analyzed from three aspects: ( 1 ) Reasons for installation of the pipeline system; ( 2 ) Environment; ( 3 ) Fluid induced.

After the initial commissioning and normal operation for a period of time, it failed during the operation. The common causes of the failure were: internal flow sensor connection layer, lightning strike, and environmental changes.

1 , internal connection layer

Because split electromagnetic flowmeters measure the chance of containing dirty bodies in the suspended solids or fouling over any other flow meter, the inner-layer connections appear to have a higher probability of failure. If the adhesion layer of conductivity and liquid conductivity is tight, the instrument can also output normal signal, only changing the circulation field, forming a hidden fault of measurement error; if the high-conductivity adhesion layer, the electromotive force between the electrodes will short circuit; if the insulating layer Connection, electrode surface insulation and disconnection circuit. Two kinds of phenomena can be the instrument does not work.

2 , lightning strike

Lightning strikes a circuit where high voltages induce transient surge currents, and instruments may damage the instrument. Lightning damage damages the instrument in three ways: power lines, excitation signals and streamlines between sensor spoon transducers. However, from the lightning damage analysis of various parts of the failure, leading to the failure of high voltage and surge currents from the control room of the power circuit, other methods. Lightning strikes separate electromagnetic flowmeters from the scene of the accident, not only failure, control room, and other instruments often appear lightning strikes at the same time. Therefore, the use of the unit knows the importance of power line control room instruments, lightning protection facilities. If there is currently a general and exploratory design unit team solve this problem.

3 , changes in environmental conditions

The main reason is the fault environment day in the commissioning phase, which is not only the intervention during the commissioning and the operation of the interference source. For example, ground fault protection is not ideal, split electromagnetic flowmeters, there is no air source plant during commissioning, and the equipment is working properly, but during operation, new sources of interference (such as point pipe or near-to-far pipe welding) interfere with normal operation. In the instrument, there is a large fluctuation in the output signal.

Second, debugging stage failure

This type of faulty electromagnetic electromagnetic flow meter and the initial commissioning, but once the fault is improved, will not appear again under the same conditions. Common faults are mainly due to the installation and commissioning period, environmental interference, and the influence of fluid characteristics. There are three reasons.

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1) Pipeline system installation

Normal electromagnetic flow sensor installation location is not the correct fault, common, such as the flow sensor is installed in the network of natural gas pipelines to facilitate the cumulative retention of high; flow sensor without any pressure, the liquid directly to the atmosphere, forming a complete measuring tube; installed in the The vertical lines are dirty and may appear empty. The installation of the flow meter is special because of potential underwater to ensure that there is no float.

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2) Environment

Main pipe stray current interference, space electromagnetic interference, large electrical machinery magnetic field interference, etc. Pipeline stray current interference usually adopts good grounding protection. Satisfactory individual measurement can be obtained, but the case tube has strong stray current (such as the electrolytic workshop The assembly line cannot be overcome either, and the unique measures of flow sensors and piping edges should be taken. Introduction of electromagnetic wave - space signal cable, usually single or multiple shielded protection, but also encountered shielding protection can not be overcome.

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3) Fluid

The liquid containing microbubbles is usually evenly distributed, does not affect the normal measurement, only the volume flow of liquid and gas combined; the bubble will increase the fluctuation of the output signal, if the large bubbles cover the entire flow through the electrode surface of the electrode, so that the signal of the electrode instantaneously breaks the circuit The output signal will produce large fluctuations.

The low-frequency ( 50 / 16 hz-50 / 6 Hz) rectangular-wave excitation split magnetic flowmeter will produce noise when the liquid contains solids exceeding a certain amount of slurry, and the output signal will also have a certain degree of fluctuation.

In two or more liquid mixing process pipes, if the conductivity of the two liquids (or between their respective electrodes and potential) is different, even before mixing the inflow flow sensor, the output signal will fluctuate.

Matching the electrode material and the test results in passivation or oxidation chemistry, the formation of an insulating film on the surface of the electrode, and electrochemical polarization, both of which interfere with normal measurements.

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