How to troubleshoot the electromagnetic flowmeter during use

How to troubleshoot the electromagnetic flowmeter during use

How to troubleshoot the electromagnetic flowmeter : 1. Check whether the working power supply voltage is correct according to the working area; 2. Whether the sensor grounding is reliable or damaged; 3. Whether the medium is full of sensors, whether there is air bubble in the medium; 4. The reading is correct, Is the measured value within the measurement range? 5. Is the terminal wiring loose? 6. Is the flow sensor soaked in water? How to check the electromagnetic flowmeter : 1. The meter has no display; 2. Check whether the power supply is connected; 3. Check if the power fuse is intact; 4. Check if the power supply voltage meets the requirements; 5. Check if the monitor contrast adjustment can be adjusted, and Whether the adjustment is appropriate. The cause of electromagnetic flowmeter failure is caused by the following aspects: environmental aspects; fluid aspects; installation aspects. Environmental reasons: usually mainly due to pipeline stray current interference, strong electromagnetic interference in space, magnetic field interference of large motors. Pipe stray current interference usually takes good single grounding protection to get satisfactory results, but if you encounter strong stray current (such as electrolysis shop piping, sometimes the peak potential Vpp induced on the two electrodes can be as high as 1V ), still Additional measures and insulation of the flow sensor and piping are required. Space electromagnetic interference is typically introduced via a signal cable and is typically protected by a single or multiple layers of shielding. Fluid reasons: The evenly distributed tiny bubbles in the liquid to be tested usually do not affect the normal operation of the electromagnetic flowmeter, but as the bubble increases, the output signal of the meter will fluctuate. If the bubble is large enough to cover the entire electrode surface, As the bubble flows through the electrode, the electrode loop is momentarily broken and the output signal appears more fluctuating. When the low-frequency square-wave excited electromagnetic flowmeter measures the solid content of too much slurry, it will also generate slurry noise, which will cause the output signal to fluctuate. When measuring mixed media, if the flow sensor is measured before the mixing is not uniform, the output signal will also fluctuate. Improper matching of the electrode material and the measured medium will also affect normal measurement due to chemical action or polarization. The electrode material should be properly selected according to the instrument selection or related manual. Installation reasons: Usually the fault is caused by incorrect installation position of the electromagnetic flow sensor. Commonly, if the sensor is installed at the point of the duct that is easy to accumulate gas, or installed on the vertical tube from top to bottom, emptying may occur; or There is no back pressure after the sensor, and the fluid is directly discharged into the atmosphere to form a non-full tube in the measuring tube. Electromagnetic flowmeter troubleshooting method: resistance method; current method; voltage method; alternative method; analog signal method; waveform method. Resistance method: (1) On-off of flowmeter power fuse and excitation insurance ; (2) On-off of signal cable and excitation cable of electromagnetic flowmeter ; (3) On-off and resistance of excitation coil of electromagnetic flowmeter ; (4) Insulation resistance of the electromagnetic flowmeter excitation coil to the ground ; (5) electrode symmetry measurement ; (6) insulation resistance of the electrode to the ground; (7) resistance value of the flowmeter power transformer. Current method: measuring flowmeter output current, excitation current, voltage method: judging working power, alternative method: if the flowmeter converter and amplifier board are interchanged, analog signal method: using analog signal generator to provide flow signal, Test flow sensor, waveform method: familiar with the test line based on the line waveform electromagnetic flowmeter inspection content: appearance inspection, converter characteristic test, measurement value calibration, measuring voltage of each part, measuring insulation resistance, confirming the circuit. When the meter is checked and adjusted due to the zero drift, it is very important to adjust the zero point ( “online zero adjustment” must stop the measured medium from flowing, which is not easy to do ) . Therefore, the online inspection often omits the inspection including the operation of the sensor, and only implements the calibration of the converter, so as to compare the online inspection result with the historical data to determine whether the instrument continues to be used, repaired or updated, and the sensor is insulated according to the measured excitation coil. The degree of deterioration determines whether it is updated or not. Verify that the electromagnetic flowmeter is abnormal by online inspection. Check the flow sensor and converter separately for the pipeline that cannot stop the flow of the medium, use the analog annunciator and other general-purpose instrument to test the converter with high calibration accuracy ( depending on the accuracy of the analog annunciator ) , and the sensor inspection with the test electrode Inductive resistance, check the excitation coil including the insulation resistance and copper resistance of the excitation connection cable, as well as the indirect method of checking the excitation current output from the converter and checking the magnetic field strength. For pipelines that can stop the flow of the medium, the inlet can be entered from the vicinity of the sensor, and the electricity level and lining contamination / deposition can be checked and cleaned. Electromagnetic flowmeter zero check of the whole machine: The flow sensor measuring tube is full of liquid and no flow. This does not have the conditions in many enterprise sites and abandons the zero check and adjustment of the whole machine, but can switch to the converter for separate zero check and adjustment. . Technically, this must be meaningful after the sensor has been checked and the insulation resistance of the sensor excitation circuit and signal circuit is normal ( both cables are included ) , otherwise the whole machine will not operate normally. Usually, the zero point of the converter is negative and the value is small. If the absolute value is greater than 5% of the full scale, it needs to be checked first, and then the adjustment is made after confirming the cause. Usually, the zero point of the electromagnetic flowmeter and the individual zero difference of the converter are less than 1% . There are many cases where the zero difference value is greater than 5% due to the user's incorrect zero adjustment operation when the pipeline valve is closed. Electromagnetic flowmeter connection cable inspection: The inspection content is to check the insulation resistance of each core of the signal line and the excitation line, and check whether the grounding of each shielding layer is intact. Electromagnetic flowmeter converter check: This check is to use the general-purpose instrument and the analog signal meter matched with the flowmeter model to replace the sensor to provide the flow signal for zero adjustment and calibration. Calibration includes zero check and adjustment, setpoint check, field current measurement, current / frequency output check, and more. It should be noted that the inspection item should be compared with the last inspection value ( or factory value ) to analyze whether it has changed or changed to meet the original measurement requirements. Electromagnetic flowmeter sensor inspection: check the excitation coil copper resistance; check the excitation coil insulation resistance; check the electrode liquid resistance; check the electrode / liquid polarization voltage; check the insulation between the signal circuit insulation and the excitation circuit / signal circuit.

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