Analysis of common faults of the hottest electroma

Analysis of common fault causes of electromagnetic flowmeter

the first type of fault in the operation of electromagnetic flowmeter is the fault of the instrument itself, that is, the fault caused by the damage of instrument structural parts or components; The second type is the failure caused by external reasons, such as improper installation, flow distortion, deposition and scaling. This chapter focuses on the application and the above-mentioned second type of external causes. According to the classification of fault occurrence period, it can be divided into: ① faults in commissioning period; ② Failure during operation. During the commissioning period, the failure occurred in the initial stage of commissioning after new installation. The main reasons are improper instrument selection or setting, improper installation of CFRTP, etc. During the operation period, the fault occurs after a period of operation. The main reasons are that impurities in the fluid adhere to the electrode lining, and new interference sources appear due to changes in environmental conditions. According to the analysis of the external source of the fault, it comes from three aspects: ① pipeline system and installation; ② Caused by environment; ③ Caused by fluid. Source ① is mainly shown in the commissioning period; Sources ② and ③ will appear during the commissioning period and operation period. The unprocessed surface of parts and accessories cut by 7 testing machine 1 should be primed and painted

I. faults during commissioning

this kind of fault occurs during the initial installation and commissioning of electromagnetic flowmeter, but once the fault is eliminated after improvement, it will generally not occur again under the same conditions. Common faults during commissioning mainly include improper installation, environmental interference and fluid characteristics

1. Pipeline system, installation and other aspects

usually the fault caused by the incorrect installation position of the electromagnetic flow sensor, such as installing the flow sensor at the high point of the pipe that is easy to accumulate trapped gas; There is no back pressure behind the flow sensor, and the liquid is directly discharged into the atmosphere, forming a non full tube in its measuring tube; If it is installed on the vertical pipe flowing from top to bottom, there may be emptying, etc

2. Environmental aspects

mainly include pipeline stray current interference, space electromagnetic wave interference, large motor magnetic field interference, etc. The interference of stray current in the pipeline can usually be measured satisfactorily by taking good separate grounding protection. However, in case of strong stray current in the pipeline (such as the pipeline in the electrolysis workshop), it may not be able to be overcome. Measures must be taken to isolate the flow sensor from the pipeline (see case 12 below). Space electromagnetic wave interference usually enters through signal cable bow I, and is usually protected by single-layer or multi-layer shielding, but it has also been encountered that shielding protection cannot be overcome (see case 10)

3. In terms of fluid

liquid contains uniformly distributed small bubbles, which usually does not affect normal measurement, but the measured volume flow is the sum of liquid and gas; The increase of bubbles will cause the output signal to fluctuate. If the bubbles are large enough to flow through the electrode to cover the entire electrode surface, and the electrode signal circuit is momentarily disconnected, the output signal will have greater fluctuations. Low frequency (50/16

hz-50/6 Hz) rectangular wave exciting electromagnetic flowmeter will produce slurry noise and output signal will fluctuate to a certain extent when the solid content in the liquid exceeds a certain content. When two or more liquids are used in the pipeline mixing process, if the conductivity of the two liquids (or the potential between each liquid and the electrode) is different, it will enter the flow sensor for flow measurement before the mixing is uneven, and the output signal will also fluctuate. Improper selection of electrode material and measured medium, resulting in chemical effects such as passivation or oxidation, the formation of insulating film on the electrode surface, and electrochemical and polarization phenomena will hinder normal measurement

II. Faults during operation

faults during operation after initial commissioning and normal operation for a period of time. Common causes of faults include: adhesion layer on the inner wall of the flow sensor, lightning and electric shock, and changes in environmental conditions

1. Inner wall adhesion layer

because the electromagnetic flowmeter has far more opportunities to measure suspended solid or dirty bodies than other flow meters, the failure probability of inner wall adhesion layer is relatively high. If the conductivity of the attachment layer is similar to that of the liquid, the instrument can still output signals normally, but changing the flow surface 1 has firmly controlled the parliamentary majority product, forming a hidden fault of measurement error; If it is a high conductivity adhesion layer, the electromotive force between electrodes will be short circuited; If it is an insulating adhesive layer, the electrode surface is insulated and the measuring circuit is disconnected. The latter two phenomena will make the instrument unable to work (see case 7)

2. Lightning shock

the instantaneous high voltage and surge current induced in the lightning strike circuit will damage the instrument if it enters the instrument. There are three ways to introduce lightning strike loss instruments: power line, flow signal line between sensors and converters and excitation line. However, from the analysis of damaged parts in lightning fault, most of the induced high voltage and surge current causing the fault are introduced from the power line of the control room, and the other two ways are less. It is also learned from the scene of the lightning accident that not only the electromagnetic flowmeter fails, but also other instruments in the control room often suffer from lightning accidents at the same time. Therefore, the importance of setting lightning protection facilities for instrument power lines in the control room should be recognized when the computer system using a single electronic experimental machine passes through the controller. At present, he has been working with design units to explore and solve this problem, such as Qilu Petrochemical Design Institute [1]

3. Changes in environmental conditions

the main reason is the fault environment in the commissioning period of the same section, but the interference source does not appear in the commissioning period and intervenes again during operation. For example, an electromagnetic flowmeter with unsatisfactory grounding protection, because there is no plant disturbance source during the commissioning period, the instrument operates normally. However, during the operation period, a new interference source (such as the pipeline near the measuring point or the pipeline welding in the distance) interferes with the normal operation of the instrument, and the output signal fluctuates greatly