In the use of electromagnetic flowmeter, the first class generally is the fault of the instrument itself, that is, the failure of the instrument structure or component damage. The second category is caused by external causes. Such as the installation of the flow distortion, deposition and scaling, etc.. Here focuses on the application of the above second types of external causes of failure.
According to the classification of the fault occurrence period, it can be divided into: 1. The commissioning period of faults in a new use after debugging early, the main reason is the improper setting of instrument selection or improper installation, etc.. The running period of the fault is in operation for a period of time, the main reason is that the impurities in the fluid are attached to the electrode lining, and the new disturbance source is caused by the change of environmental conditions.
According to the source of the failure analysis from the 3 aspects: the pipeline system and the installation and other aspects of the cause of the environment. The source is mainly in the period of commissioning; the source II and the operating period will appear in the commissioning period.
One, running time fault
After the initial commissioning and normal operation of a period of time after the failure of the operation, the common failure causes are: the flow sensor wall attached layer, electric shock, environmental conditions.
1, inner wall attachment layer
Because the electromagnetic flow meter measuring the opportunity of the suspended solid or dirty body is much higher than other flow instruments, the probability of failure in the inner wall of the inner wall is relatively high. If the attachment layer conductivity and the conductivity of liquid is similar, instrument is also the normal output signal, just change the flow area, the formation of the measurement error of the hidden fault; if high conductivity adhesive layer, electrode emf will is short; if the insulation adhesive layer, the electrode surface is insulated and measuring circuit is disconnected. After two phenomena will make the instrument can not work.
2, thunder electric shock
Lightning strikes in the line of the instantaneous high voltage and surge current, into the instrument will damage the instrument. Lightning strike loss meter has 3 ways: the introduction of power line, traffic signal line between the sensor and the line excitation converter. However, from the analysis of the damaged parts of the lightning fault, the induced high voltage and surge current of the fault are introduced from the control room, the other two channels are less. Also from the occurrence of lightning accident scene learned that not only the electromagnetic flowmeter in the control room in the same time, the electric accident. Therefore, the use of units to understand the importance of setting control room instrument power line lightning protection facilities. The incumbent has several design units team knowledge and solve this problem.
3, environmental conditions change
The main reason is that in the last section of the debugging of the fault environment, but the source is not in the commissioning period and the operation of the intervention. For example, a grounding protection is not ideal for electromagnetic flowmeter, commissioning period due to the non factory disturbance source, the instrument is normal, but in the operating period of the new interference sources (such as measurement points near the pipeline or pipeline welding) to interfere with the normal operation of the instrument, the output signal amplitude fluctuations.
Two, debugging phase fault
This type of fault in the initial installation of the electromagnetic flowmeter is used to debug, but an improved troubleshooting, later in the same conditions generally will not appear again. There are three main reasons for the failure of the common debugging period, the installation is improper, the environmental disturbance and the characteristics of the fluid.
1, pipe system and installation, etc.
Is usually electromagnetic flow sensor installation location of fault caused by the incorrect, common such as the flow sensor is installed in the network high easy accumulation of gas retention; no back pressure flow sensor, liquid Jing straight row atmosphere, formation of the measuring tube non full pipe; installed in the self to the downstream of the vertical pipe may evacuation etc., open channel flow meter installation is more special, because it is latent and water, so to ensure no floating.
2, environmental aspects
The main channel is the stray current interference, the space electromagnetic interference, the magnetic field disturbance of the large motor. The stray current interference of the duct is usually taken good measure, but it is not certain to be able to overcome the strong stray current (such as the electrolytic plant pipe). Space electromagnetic wave interference - like the introduction of signal cable, usually a single or multi-layer shielding to be protected, but also has encountered a shield protection can not overcome.
3, fluid
The liquid containing small bubbles usually does not affect the normal measurement, but the measured volume flow is both liquid and gas, and the bubble increase can make the output signal fluctuation. If the bubble is large enough to cover the electrode surface, the electrode signal circuit is disconnected and the signal will be more volatile.
Low frequency 50/16Hz-50/6Hz rectangular wave excitation electromagnetic flow meter measuring liquid containing solid content exceeds a certain value will be generated when the slurry noise, the output signal will also have a certain degree of fluctuation.
Two or more than two kinds of liquid for pipeline mixing process, if two kinds of liquid conductivity (or their respective with the electrode potential) are different, before the mixed into the flow sensor for flow measurement, the output signal will produce fluctuations.
The electrode material is not properly selected, and the electrode material is not properly selected. It can be formed on the surface of the insulating film and the electrochemical and polarization phenomena.
