Environmental reasons: usually mainly caused by stray current interference in pipelines, strong electromagnetic wave interference in space, magnetic field interference from large motors, etc.
How to troubleshoot problems when the electromagnetic flowmeter is used:
How to troubleshoot problems with the electromagnetic flowmeter:
1. Check the working power supply voltage according to the working area. Is it correct?
2. Is the sensor grounding reliable or damaged?
3. Is the medium full of the sensor and whether there are bubbles in the medium?
4. The reading is correct No, is the measured value within the measurement range?
5. Are the terminal wiring loose?
6. Is the flow sensor soaked in water?
How to troubleshoot problems with electromagnetic flowmeters:
1. The meter has no display; 2. Check whether the power supply is connected; 3. Check whether the power fuse is intact;
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; and installation aspects. Environmental reasons: usually mainly caused by stray current interference in pipelines, strong electromagnetic wave interference in space, magnetic field interference from large motors, etc. For stray current interference in pipelines, satisfactory results can usually be obtained with good single grounding protection. However, if a strong stray current is encountered (such as electrolytic workshop pipelines, sometimes the peak AC potential Vpp induced on the two currents can be as high as 1V), it is still possible to obtain satisfactory results. Additional measures and flow sensors and pipe edges need to be taken. Space electromagnetic wave interference is generally introduced through signal cables and is usually protected by single or multi-layer shielding. Fluid reasons: The measured liquid contains evenly distributed tiny bubbles, which usually do not affect the normal operation of the electromagnetic flowmeter. However, as the bubbles increase, the instrument output signal will fluctuate. If the bubbles are large enough to cover the entire electrical surface, As the bubbles flow through the electricity, the electrical circuit will be instantly disconnected and the output signal will fluctuate even more. When an electromagnetic flowmeter with low-frequency square wave excitation measures slurry with excessive solid content, it will also produce slurry noise, causing the output signal to fluctuate. When measuring mixed media, if the flow sensor is entered for measurement before the mixture is uniform, the output signal will also fluctuate. Improper matching of electrical materials and measured media will also affect normal measurement due to chemical effects or chemical phenomena. Electrical distribution materials should be selected correctly according to instrument selection or relevant manuals. Installation reasons: Usually the fault is caused by the incorrect installation position of the electromagnetic flow sensor. Common ones include installing the sensor at a piping point where gas is likely to accumulate; or installing it on a top-down vertical pipe, which may cause emptying; or There is no back pressure behind the sensor, and the fluid is directly discharged into the atmosphere, resulting in 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 and off of the flow meter power fuse and excitation fuse; (2) On and off of the electromagnetic flow meter signal cable and excitation cable; (3) On and off of the electromagnetic flow meter excitation coil and resistance value; (4) Insulating resistance of electromagnetic flowmeter excitation coil to ground; (5) Electrical symmetry measurement; (6) Electrical insulating resistance to ground; (7)The resistance of the flowmeter power transformer. Current method: measure the output current and excitation current of the flow meter; voltage method: determine the working power supply; substitution method: such as exchanging the converter and amplifier board of the flow meter; analog signal method: use an analog signal generator to provide the flow signal to Test the flow sensor, waveform method: Test the key points of the waveform electromagnetic flowmeter based on familiarity with the circuit. The inspection contents include: appearance inspection, converter performance test, measurement value calibration, measuring the voltage of each part, measuring the insulating resistance, confirming the circuit, etc.
Due to the zero point drift during instrument inspection and adjustment, it is very important to adjust the zero point ("online zero adjustment" must stop the flow of the measured medium, which is not easy to achieve in practice). Therefore, online inspections often omit inspections that include sensor operation, and only perform calibration of the converter so that the online inspection results can be compared with historical data to determine whether the instrument should continue to be used, repaired, or updated. For sensors, the measured excitation coil insulating resistance is The degree of deterioration determines whether to update or not. Verify whether there are any abnormalities in the electromagnetic flowmeter through online inspection. For pipelines that cannot stop the flow of media, check the flow sensor and converter respectively. Use an analog annunciator and other general instruments to test the converter to have a higher calibration degree (depending on the analog annunciator degree). The sensor inspection is to test the electrical contact liquid. Resistance, check the excitation coil including the insulating resistance and copper resistance of the excitation connecting cable, as well as check the excitation current output by the converter, check the magnetic field strength and other indirect methods. For pipelines that can stop the flow of media, you can enter from the preset entrance hole near the sensor to check the electrical level and lining contamination/deposition conditions and clean them.
Zero point check of the entire electromagnetic flowmeter machine: The flow sensor measuring tube is filled with liquid and there is no flow. This is not possible at many companies' sites and they give up the zero point check and adjustment of the whole machine. However, they can instead perform a single zero point check and adjustment of the converter. . Technically speaking, this has practical significance only after the sensor inspection is completed and the insulating resistance of the sensor excitation circuit and signal circuit are normal (both including cables), otherwise the whole machine will not operate normally. Usually the single zero point of the converter is a negative value, and the value is also very small; if the value is greater than 5% of the full scale, it needs to be checked first, and then adjusted after the cause is confirmed. Normally, the difference between the zero point of the electromagnetic flowmeter and the zero point of the converter is less than 1%. In many cases, zero point difference values greater than 5% are caused by users performing incorrect zero adjustment operations when pipeline valves are not properly closed. Inspection of the electromagnetic flowmeter connecting cable: The inspection content is to check the conduction resistance of each core of the signal line and the excitation line, and to check whether the grounding of each shielding layer is intact.
Electromagnetic flowmeter converter inspection: The content of this inspection is to use a general instrument and an analog annunciator matching the flowmeter model instead of the sensor to provide the flow signal for zero adjustment and calibration. Calibration includes zero point check and adjustment, set point 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 are changes or whether the changes meet the original measurement requirements. Electromagnetic flowmeter sensor inspection: check the copper resistance of the excitation coil;Check the insulating resistance of the excitation coil; check the electrical resistance to liquid; check the voltage between electricity and liquid; check the insulating resistance of the signal circuit and the insulating edge of the excitation circuit/signal circuit.
Hangzhou Economic Development Area，Hangzhou 310018，China
