How to troubleshoot problems with electromagnetic flowmeters: 1. According to the working area, check whether the working power supply voltage is correct; 2. Whether the grounding of the sensor is reliable or damaged; 3. Whether the medium is full of the sensor, and whether there are bubbles in the medium; 4. Is the reading correct? Is the measurement value within the measurement range? 5. Is the terminal wiring loose? 6. Is the flow sensor immersed in water?How to check if there is a problem with the electromagnetic flowmeter: 1. The instrument has no display; 2. Check whether the power is on; 3. Check whether the power fuse is in good condition; 4. Check whether the power supply voltage meets the requirements; 5. Check whether the display contrast adjustment can be adjusted and whether the adjustment is appropriate.The causes of electromagnetic flowmeter failure are caused by the following aspects: environmental aspects; fluid aspects; installation aspects. Environmental reasons: It is usually mainly caused by pipeline stray current interference, strong electromagnetic wave interference in space, and magnetic field interference of large electric motors. Pipeline stray current interference usually takes good separate grounding protection to obtain satisfactory results, but if it encounters strong stray currents (such as electrolytic workshop pipelines, sometimes the peak value of AC potential Vpp induced on the two electrodes can be as high as 1V), it is still Additional measures and insulation between the flow sensor and the pipeline are required. Space electromagnetic wave interference is generally introduced through signal cables, and is usually protected by single-layer or multi-layer shielding.Fluid reasons: the measured liquid contains evenly distributed tiny bubbles usually does not affect the normal operation of the electromagnetic flowmeter, but as the bubbles increase, the output signal of the meter will fluctuate. If the bubbles are large enough to cover the entire electrode surface, As the bubbles flow through the electrode, the electrode circuit will be cut off instantaneously and the output signal will have greater fluctuations. When the electromagnetic flowmeter with low frequency square wave excitation measures the slurry with too much solid content, it will also produce slurry noise, which will cause the output signal to fluctuate. When measuring mixed media, if the flow sensor is used for measurement before the mixing is not uniform, the output signal will also fluctuate. Improper selection of the electrode material and the measured medium will also affect the normal measurement due to chemical effects or polarization phenomena. The electrode material should be correctly selected according to the instrument selection or relevant manuals.Installation reasons: usually caused by the incorrect installation position of the electromagnetic flow sensor, such as installing the sensor on a piping point where gas is easy to accumulate; or installing it on a vertical pipe from top to bottom, which may be drained; or There is no back pressure behind the sensor, and the fluid is directly discharged into the atmosphere to form a non-full tube in the measuring tube.Electromagnetic flowmeter troubleshooting methods: resistance method; current method; voltage method; substitution method; analog signal method; waveform method. Resistance method: (1) On-off of flowmeter power supply fuse and excitation fuse; (2) On-off of electromagnetic flowmeter signal cable and excitation cable; (3) On-off and resistance value of electromagnetic flowmeter excitation coil; (4) The insulation resistance of the excitation coil of the electromagnetic flowmeter to the ground; (5) Electrode symmetry measurement; (6) The insulation resistance of the electrode to the ground; (7) The resistance value of the flowmeter power transformer. Current method: measure the output current and excitation current of the flowmeter, voltage method: judge the working power source, alternative method: such as interchange the converter and amplifier board of the flowmeter, analog signal method: use an analog signal generator to provide a flow signal to Test flow sensor, waveform method: on the basis of familiarity with the circuit, test the key points of the waveform electromagnetic flowmeter. The inspection content includes: appearance inspection, converter characteristic test, measurement value calibration, measuring voltage of each part, measuring insulation resistance, confirming circuit, etc. It is very important to adjust the zero point due to the zero drift during the inspection and adjustment of the instrument (“online zero adjustment” must stop the flow of the measured medium, which is not easy to do in practice).Therefore, online inspections often omit inspections that include sensor operation, and only implement calibration of the converter, so as to compare the online inspection results with historical data to determine whether the meter is to be used, repaired or updated. For the sensor, the insulation resistance of the excitation coil is measured. The degree of deterioration determines whether it is updated or not. Check whether the electromagnetic flowmeter is abnormal or not through online inspection. Check the flow sensor and converter separately for pipelines that cannot stop the flow of the medium. Use analog annunciators and other general instruments to test the converter with high calibration accuracy (this depends on the accuracy of the analog annunciator), and test the electrode for sensor inspection. Wet resistance, check the excitation coil, including the insulation resistance and copper resistance of the excitation connection cable, and check the excitation current output by the converter, check the magnetic field strength and other indirect methods. For pipelines that can stop the medium flow condition, it can be entered from the preset hole near the sensor to check and clean the electrical level and lining contamination/sediment status.Electromagnetic flowmeter complete machine zero point inspection: The flow sensor measuring tube is filled with liquid and has no flow. This is where the conditions are not available in many companies and give up the zero point inspection and adjustment of the complete machine, but the converter can be replaced with a separate zero point inspection and adjustment . Technically speaking, this must be of practical significance only after the sensor inspection is completed and the insulation resistance of the sensor excitation circuit and signal circuit is normal (both include cables), otherwise the whole machine will not operate normally. Usually, the single zero point of the converter is negative, and the value is also very small; if its absolute value is greater than 5% of the full scale, it needs to be checked first, and then adjusted after the cause is confirmed. Under normal circumstances, the difference between the zero point of the whole electromagnetic flowmeter and the zero point of the converter alone is less than 1%. There are many cases where the zero difference value greater than 5% is caused by the user’s incorrect zero adjustment operation when the pipeline valve is not closed properly.Electromagnetic flowmeter connecting cable inspection: the inspection content is to check the signal wire and the excitation wire core conduction insulation resistance, check whether the grounding of each shielding layer is intact.Electromagnetic flowmeter converter inspection: The content of this inspection is to replace the sensor with a general-purpose instrument and an analog annunciator that matches the flowmeter model to provide flow signals for zero adjustment and calibration. Calibration includes zero check and adjustment, set value check, excitation current measurement, current/frequency output check, etc. It should be noted that the inspection items should be compared with the last inspection value (or factory value) to analyze whether there is any change or whether the change meets the original measurement requirements.Electromagnetic flowmeter sensor inspection: check the copper resistance of the excitation coil; check the insulation resistance of the excitation coil; check the electrode contact resistance; check the polarization voltage between the electrodes/liquid; check the insulation of the signal circuit and the insulation between the excitation circuit/signal circuit.
Post time: 21-09-21