LD-100S electromagnetic flowmeter failure causes and troubleshooting methods

The causes of LD-100S electromagnetic flowmeter failure are caused by the following aspects: environment, fluid, and installation. Environmental reasons: usually mainly stray current interference in pipelines, strong electromagnetic wave interference in space, magnetic field interference from large motors, etc. Pipeline stray current interference usually requires good independent grounding protection to obtain satisfactory results. However, if a strong stray current is encountered (such as electrolytic workshop pipelines, sometimes the AC potential peak value Vpp induced on the two electrodes can be as high as 1V), it is still possible to obtain satisfactory results. Additional measures need to be taken to insulate the flow sensor from the pipeline. 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 electrode surface, As the bubbles flow through the electrode, the electrode circuit will be instantly disconnected, causing greater fluctuations in the output signal. 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 selection of electrode material and measured medium will also affect normal measurement due to chemical effects or polarization phenomena. The electrode material should be correctly selected according to the instrument selection or relevant manual. Installation reasons: Usually the fault is caused by incorrect installation position of the electromagnetic flow sensor. Common problems include installing the sensor at the highest point of the piping system where gas is likely to accumulate; or installing it on a vertical pipe from top to bottom, 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.

LD-100S electromagnetic flowmeter troubleshooting methods: resistance method, current method, voltage method, substitution method, analog signal method, waveform method, resistance method: (1) Flow meter power supply fuse, 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) Insulation resistance of electromagnetic flowmeter excitation coil to ground; (5) Electrode Symmetry measurement; (6) Insulation resistance of electrode to ground; (7) Resistance of flow meter 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 characteristic test, measurement value calibration, measuring the voltage of each part, measuring the insulation 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 involving sensor operation, and only implement calibration of the converter so that the online inspection results and historical data can be combined.Based on the comparison, it is determined whether the instrument should be continued to be used, repaired or updated. For the sensor, it is determined whether to update or not based on the measured deterioration of the insulation resistance of the excitation coil. 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 degree of calibration (depending on the degree of the analog annunciator). For sensor inspection, test the electrode for liquid contact. Resistance, check the excitation coil including the insulation 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.