的一般保养： General maintenance of electromagnetic flowmeter :
1) Frequently observe the sensor power cable and transmission cable (or wire) for damage and aging, and protect the rubber sheath outside the cable. 2) Regularly (usually half a year) scrub the electrode surface with a soft cloth to remove dirt or deposits. 3) Remove the debris in the straight pipe section upstream of the sensor.
Maintenance and repair of electromagnetic flowmeter
The failures often encountered in the use of electromagnetic flow meters, the first type is generally the failure of the instrument itself, that is, the failure caused by the damage to the instrument structure or components; the second type is caused by external reasons. Such as improper installation, flow distortion, deposition and scaling. The focus here is on the application side and the above-mentioned second category of external cause failures. According to the classification of faults, they can be divided into: ① faults during operation; ② faults during commissioning. Faults during commissioning occur in the early stage of commissioning after new installation. The main reasons are improper selection or setting of the instrument and improper installation. Faults during operation occur after a period of operation. The main reasons are impurities in the fluid adhering to the electrode lining, and new interference sources due to changes in environmental conditions. According to the external source of the failure, it comes from three aspects: ① caused by the pipeline system and installation; ② caused by the environment; ③ caused by the fluid. The source ① is mainly displayed during the commissioning period; the sources ② and ③ will appear during the commissioning and operation periods.
1. Failure during operation
Faults that occur during operation after initial commissioning and normal operation for a period of time. Common causes of failure include: adhesion layer on the inner wall of the flow sensor, lightning strike, and changes in environmental conditions.
1. The inner wall adhesion layer. Because the electromagnetic flowmeter has a greater chance of measuring suspended solids or dirt than other flow meters, the probability of failure caused by the inner wall adhesion layer is relatively high. If the conductivity of the adhesion layer is similar to the conductivity of the liquid, the meter can still output signals normally, but only change the flow area to form a hidden fault of the measurement error. If it is a high conductivity adhesion layer, the electromotive force between the electrodes will be short-circuited; The electrode surface is insulated to disconnect the measuring circuit. The latter two phenomena make the meter inoperable. 2. Lightning and electric shocks induce instantaneous high voltage and surge current in the line, and entering the meter will damage the meter. There are three ways to introduce the lightning damage instrument: the power line, the flow signal line and the excitation line between the transducer and the transducer. However, from the analysis of the damaged parts in the lightning fault, most of the induced high voltage and surge current that caused the failure were introduced from the power line in the control room, and the other two paths were less. It was also learned from the scene of the lightning strike that not only the electromagnetic flowmeter failed, but also other instrumentation and electricity in the control room often had lightning strikes at the same time. Therefore, users should recognize the importance of setting lightning protection facilities for control room instrument power lines. The incumbent already knows and explores how to solve this problem. 3. Changes in environmental conditions, the main reason is the same as the fault environment in the debugging period, except that the interference source does not appear during the debugging period, and then intervenes during the operation. ，调试期因无厂扰源，仪表运行正常，然而在运行期出现新干扰源（例如测量点附近管道或较远处实施管道电焊）干扰仪表正常运行，出现输出信号大幅度波动。 For example, an electromagnetic flowmeter with unsatisfactory grounding protection. During the commissioning period, there is no source of interference from the factory, and the instrument operates normally. However, during the operation period, new interference sources (such as pipelines near the measurement point or remotely implemented pipeline welding) interfere with the instrument. During operation, the output signal fluctuates greatly.
Failure during commissioning
This type of fault occurs when the electromagnetic flowmeter is initially installed and debugged, but once it is improved to eliminate the fault, it will generally not reappear under the same conditions in the future. Common failures during commissioning are mainly caused by improper installation, environmental interference, and fluid characteristics. 1. In the pipeline system and installation, it is usually caused by the incorrect installation position of the electromagnetic flow sensor. Commonly, for example, the flow sensor is installed at the high point of the pipeline network that is liable to accumulate retained gas. Discharge into the atmosphere to form a non-full pipe in the measuring tube; installed on a vertical pipe that flows downward from the top, emptying may occur, etc. The installation of an open channel flowmeter is special. Since it is submerged and underwater, it must be guaranteed to have no floating. 2. In terms of environment, it is mainly the stray current interference of pipelines, electromagnetic interference in space, and magnetic interference of large motors. Pipeline stray current interference can usually be satisfactorily measured by good separate grounding protection. However, if the pipeline has strong stray current (such as the pipe in the electrolytic workshop), it may not be overcome, and measures must be taken to isolate the flow sensor from the pipeline. Space electromagnetic interference-generally introduced through signal cables, usually protected by single or multiple layers of shielding, but also encountered shielding protection can not be overcome. 3. In terms of fluids, the liquid contains evenly distributed fine air bubbles, which usually does not affect the normal measurement, but the measured volume flow is the sum of both liquid and gas; the increase of air bubbles will cause the output signal to fluctuate. On the surface, the electrode signal loop is instantly disconnected, and the output signal will have greater fluctuations. Low-frequency (50 / 16Hz-50 / 6Hz) rectangular wave excitation electromagnetic flowmeter will measure the noise of solids in the liquid when it contains more than a certain content, which will produce slurry noise, and the output signal will fluctuate to some extent. 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 not uniform, and the output signal will also fluctuate. Improper selection of the electrode material and the measured medium will cause chemical effects such as passivation or oxidation, the formation of insulating films on the electrode surface, and electrochemical and polarization phenomena, which will prevent normal measurement
的一般故障及其排除： General fault of electromagnetic flowmeter and its elimination:
1) There is output when the liquid is not flowing: 1. The signal transmission cable between the converter and the converter has an open circuit; 2. The signal cable is disconnected from the electrode; 3. The electrode surface is contaminated or an insulating layer is deposited; 4. Poor ground or open circuit. Solution: 1. Connect the cable; 2. Turn on the sensor and reconnect it; 3. Scrub the electrode surface; 4. Connect the ground wire. 2) No output of liquid flow: 1. The two core wires of the signal transmission cable between the converter and the converter are reversed; 2. The power supply is not connected or the connection is poor; 3. There is leakage in the sensor instrument pipeline, housing, and end surface. Solution: 1. Reverse the cable head; 2. Connect the power supply and maintain good contact; 3. Repair the sensor. 3) The output is unstable: 1. The flow field is unstable; 2. The liquid passing through the sensor contains gas and large solid blocks; 3. The electrical connection is virtual; 4. The ground is poor; 5. The electrode is leaking, the solution is: 1. Modify the pipeline or increase the installation of fake sensors; 2. normal phenomenon; 3. check the wiring and connect the line; 4. connect the ground line; 5. repair the sensor. 4) Excessive error: 1. The zero point is too high; 2. It is not completely filled with liquid; 3. The power supply is distorted too much; 4. The grounding is poor. Solution: 1. Readjust the zero point; 2. Improve the pipeline conditions, the sensor is always filled with liquid; 3. Improve the power supply conditions to meet normal working conditions; 4. Connect the ground wire.