Electromagnetic flowmeter treatment of common problems in sewage measurement

Published on by

The electromagnetic sewage flowmeter is buried underground with the pipeline. The sensor has IP68 protection structure. The converter is installed in the instrument box or indoors. The two are connected by cables. Due to the ground subsidence, the mountain environment is humid, and so on, the sensors and converters are not Thoroughly handle moisture (waterproof) at the cable joints. It coincides with the fact that the joint is in a humid environment, such as instrument wells, cable trenches, etc., and moisture intrusion into the cable joints has the following possibilities:
(1) The insulation coil is insulated from the ground, resulting in a small measurement result;
(2) The contact resistance of the excitation circuit cable connection becomes large, so that the excitation circuit of the converter is in a non-constant current working area, and the excitation current is decreased, which also causes the measurement result to be small. If the contact resistance is unstable, the measured value fluctuates.
(3) The signal line is grounded to the ground, causing signal attenuation, and finally the measurement result is small.
(4) The insulation performance of the signal line excitation line to the ground is degraded, so that the measurement result is much larger than the normal data. If the interference is unstable, the influence on the hot water flow meter instrument also changes, and then the fluctuation occurs;
(5) The contact resistance of the signal cable connection becomes larger, so that the measured value becomes smaller. If the contact resistance is unstable, the measured value cannot be stabilized, and interference is easily introduced;
The above abnormal situation occurs because it occurs in the signal loop. It is difficult to judge. Only when it is in the field, after troubleshooting other possible problems of the circulating water flow meter, it should be checked whether there is any problem with the cable. The field instrument maintenance personnel only need to measure the field loop resistance. The value is compared with the data provided by the manufacturer, the grounding resistance is tested, the problem is determined step by step, and measures are taken, or the entire cable is replaced, or the cable joint is kept dry.
The sewage electromagnetic flowmeter is basically not in operation for more than one year after being put into operation, but after one year, there will often be abnormal work, which is manifested by the measurement value becoming larger or smaller, or constantly fluctuating, and On-site inspection has ruled out the possibility that the pipeline is not full, and the medium contains gas. It is also possible that such problems may be related to cable faults.
First, the sewage electromagnetic flowmeter has no flow output
1. Cause Analysis Such faults are more common during use. The reasons are generally: (1) the meter is not powered properly; (2) the cable connection is not normal; (3) the medium flow condition does not meet the installation requirements; (4) the sensor zero Parts are damaged or the lining has an adhesive layer; (5) The converter components are damaged.
2, the solution
(1) Confirm that the power has been connected, check whether the voltage of each output of the power circuit board is normal, or try to replace the entire power circuit board to judge whether it is good or bad.
(2) Check if the cable is intact and the connection is correct.
(3) Check the flow direction of the measured medium and whether the medium inside the tube is full. For sewage electromagnetic flowmeters that can measure forward and reverse, if the direction is inconsistent, it can be measured, but the set display flow does not match the positive and negative directions and must be corrected. If the sensor is too large, you can change the direction of the arrow on the sensor and reset the display meter symbol. If the pipeline is not full of media, it is mainly caused by improper installation of the sensor. Measures should be taken during installation and installed strictly according to the installation requirements to avoid causing the medium in the pipeline to be dissatisfied.
(4) Check whether the electrode on the inner wall of the transmitter is covered with a layer of dielectric crucible. For the measurement medium that is easy to scab, it should be cleaned regularly.
(5) If it is determined that the converter component is damaged due to damage, replace the damaged component.
Second, the output value fluctuations
1, the cause analysis
Most of these failures are caused by the measurement medium or the external environment. For example, strong magnetic fields and strong electromagnetic waves are generally taken away from strong magnetic fields when installed. The sewage electromagnetic flowmeter shall comply with the electromagnetic compatibility requirements and work normally under the specified radiated electromagnetic field environment, and the instrument performance will not be degraded or the work may be abnormal under this environment. In addition, strong radio waves and stray currents on the pipeline may also be sources of interference. The fault can be eliminated by itself after the external interference is removed. In order to ensure the accuracy of the measurement, such failures can not be ignored. In some production environments, the vibration of the measuring pipe or liquid is large, which may cause the circuit board's circuit board to loosen, which may also cause fluctuations in the output value.
2, the solution
(1) Confirm whether it is the cause of the operation of the process personnel, the fluid does pulsate, and the flow meter only reflects the flow condition as it is, and the fault can be eliminated by itself after the pulsation ends.
(2) Electromagnetic interference generated by external currents and the like. Check whether the instrument is in a working environment with large electrical appliances or welding machines. Make sure that the instrument is grounded and the operating environment is good.
(3) After the sewage electromagnetic flowmeter is properly grounded, the influence of most of the stray current of the pipeline can be avoided.
(4) When the pipe is not filled with the liquid to be tested or the bubble contains bubbles, both are caused by the process. At this point, the process technician can be requested to confirm that the output value can be restored after the liquid is full or the bubble is recovered.
(5) The transmitter circuit board is a plug-in structure. Due to the large vibration of the pipeline or liquid in the field, the power supply board of the flowmeter is often loosened. If loose, remove the flowmeter transmitter and re-attach the board.
3. The value of the sewage electromagnetic flowmeter does not match the actual value.
1, the cause analysis
(1) Whether the transmitter circuit board is intact; (2) When the liquid flow rate is too low, the measured liquid contains tiny bubbles, and the bubble rises gradually gathers above the pipeline, and the liquid circulation area changes, and the gas may interfere for a long time. The signal affects the measurement accuracy; 3) The signal cable is not well connected or the insulation performance of the cable is reduced during use, resulting in inaccurate measurement; (4) The parameter setting value of the converter is not accurate.
2, the solution
(1) Check if the transmitter circuit board is intact. If the junction box is ingress or corroded by corrosive liquids, electrical performance may be degraded or damaged. The board should be replaced at this time.
(2) Ensure that the flow rate of the liquid to be measured in the pipeline is above the minimum flow limit to enable the transmitter to work properly.
(3) Check the signal cable connection and the insulation performance of the cable. If the signal cable is loose, reconnect it; if the insulation of the cable is found to meet the insulation requirements, a new cable is required.
(4) Re-set the converter set value and check the zero and full scale values ​​of the converter.
Fourth, the sewage electromagnetic flowmeter output signal super full range
1, the cause analysis
The causes of such failures are: (1) the signal cable wiring is wrong or the cable connection is broken; (2) the converter's parameter setting is incorrect; (3) the converter and the sensor model are not matched.
2, the solution
(1) Check if the signal loop connection is normal or not. If the signal loop is disconnected, the output signal will be overfull. In this case, the signal cable should be reconnected correctly. At the same time, it is necessary to check whether the insulation performance of the cable is intact. If it does not meet the requirements, a new cable needs to be replaced.
(2) Detailed inspection of the parameters of the sewage electromagnetic flowmeter converter and whether the zero point and full scale meet the requirements.
(3) If it is checked that the model of the converter and the sensor are not matched, you need to contact the factory for exchange.
Five, zero instability
1, the cause analysis
(1) The pipe is not filled with liquid or contains bubbles in the liquid.
(2) Subjectively, there is no flow in the tube pump liquid and there is actually a slight flow.
(3) Reasons for liquids (such as poor conductivity of liquid conductivity, electrode contamination, etc.).
(4) The water in the terminal box or the excitation coil is damp, so that the excitation coil circuit is insulated from the ground.