Analysis of failures encountered in the use of electromagnetic flowmeters
Frequently encountered failures in the use of electromagnetic flowmeters, the first is the common failure of the instrument itself, that is, damage to the structure or components of the instrument; the second is the external cause. Such as installation and flow field distortion, deposition and scaling. The focus is on the second category and the cause of the application failure. According to the classification problems, they can be divided into: (1) Faults during operation; (2) Faults in the debugging phase. Faults often encountered in the use of electromagnetic flowmeters. The first is the common fault of the instrument itself, that is, the structure or components of the instrument cause damage to the fault. ; Secondly, it is caused by external causes. Such as installation and flow field distortion, deposition and scaling. The focus is on the second category and the cause of the application failure. According to the classification problem, it can be divided into: (1) failure during operation; (2) failure during debugging. In the early debugging stage, the main reason is that the selection or setting of tools is unreasonable, the installation error, and the period after the running foot fails during the operation. The main reason is that the fluid inclusion is attached to the electrode Li Ning, and the environment changes. New sources of interference, etc. According to the external source of the fault, analyze from three aspects: (1) the reason for the installation of the piping system; (2) the environment; (3) the fluid caused. failure, operating cycle after the initial debugging and normal operation for a period of time, it fails during the operation process. The common causes of failure are: internal flow sensor connection layer, lightning strikes, and environmental changes. . 1, the internal connection layer Because the electromagnetic flowmeter measures a suspended solid phase or a dirty body than any other flowmeter, the probability of failure of the internal connection is higher. If the conductivity and liquid conductivity are attached to the layer tightly, the instrument can still output the signal normally, but the flow area is changed, forming a hidden fault of measurement error; if the high conductivity is attached to the layer, the electromotive force between the electrodes will be short-circuited; if the insulating layer Connect, insulate the electrode surface and disconnect the circuit. Both phenomena can make the instrument unable to work. 2, lightning strikes lightning strikes the circuit, high voltage induced transient surge current, to the instrument may damage the instrument. There are three ways to damage the instrument by lightning: the power line, the excitation signal between the sensor and the spoon converter, and the flow line. However, from the lightning damage analysis of the failure of each component, the introduction of high voltage and surge current from the control room's power supply circuit, other ways that lead to failure. Lightning strikes the electromagnetic flowmeter from the accident site, not only fails, but also in the control room, lightning strikes often occur at the same time in other instruments. Therefore, the user knows the importance of power line control room instruments and lightning protection facilities. If there is currently a general and exploratory design unit team to solve this problem. 3, the change in environmental conditions is mainly due to the failure of the environment during the debugging phase, not just the intervention during the debugging period and the interference source's operation process. For example, the ground fault protection is not ideal, the electromagnetic flowmeter, there is no air source plant during the debugging, and the equipment is working normally, but during the operation, the new interference source (such as the welding of the spot pipe or the near and far pipe) interferes with the normal operation of the instrument , The output signal has large fluctuations. Secondly, the failure of the electromagnetic flowmeter during the debugging stage is related to preliminary debugging. However, once the failure is improved, it will generally not reappear under the same conditions. Common faults are mainly due to the installation and commissioning period, environmental interference, and the impact of fluid characteristics. There are three reasons. 1. Pipeline system installation and other common electromagnetic flow sensor installation position is not correct faults. For example, the flow sensor is installed in a natural gas pipeline network that is easy to accumulate and retain high; the flow sensor does not have any pressure, and the liquid is directly discharged into the atmosphere, forming a complete Measuring tube; installed in the vacancy that may occur due to the dirty vertical line, the installation of the flow meter is special because of the potential underwater to ensure that there is no floating. 2. Environmental main pipeline stray current interference, space electromagnetic wave interference, large motor magnetic field interference, and other pipeline stray current interference usually take good grounding protection and can be satisfactorily measured separately, but in case the pipe has a strong stray current ( Such as the assembly line of the electrolysis workshop) cannot be overcome, and unique measures should be taken for the flow sensor and the pipe edge. Electromagnetic wave-space signal cable introduction, usually single or multiple shielding protection, but also encountered shielding protection can not be overcome. 3. The fluid liquid contains tiny bubbles usually evenly distributed and does not affect the normal measurement. Only the volume flow liquid and gas are combined; the bubbles will increase the fluctuation of the output signal. If the large bubbles cover the entire surface of the electrode flowing through the electrode, the signal of the electrode will be instantaneous If the circuit is disconnected, the output signal will produce large fluctuations.
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