Thread Content
An electromagnetic flowmeter is a flow measurement instrument that operates based on the law of electromagnetic induction. An electromagnetic flowmeter consists of a transmitter and a converter. An electromagnetic flow transmitter converts changes in flow rate into changes in induced electromotive force. The converter amplifies the weak induced potential and converts it into a unified standard signal for output, so as to enable remote indication, recording, accumulation, and regulation. It can measure the volumetric flow rate of liquids or liquid-solid mixtures with a certain conductivity, and is often used to measure the flow rate of acids, bases, salts, and liquids containing solid particles – this is what gives it an advantage over other flow meters. Use and maintenance of electromagnetic flowmeters: ① The transmitter should be installed in a location within the pipe where it is always filled with liquid, to avoid the illusion that the pointer is not at zero when there is no liquid in the pipe. It should generally be installed vertically to prevent errors caused by bubbles forming as liquid flows past the electrodes. ②The signal from electromagnetic flowmeters is relatively weak, typically ranging from 2.5 to 8 mV; especially when the flow rate is low, it is only a few microvolts. Therefore, special attention must be paid to the impact of external interference on the measurement accuracy when using such devices. Therefore, the transmitter’s enclosure, shield wire, measurement wires, and the pipes at both ends of the transmitter must all be connected to a separate grounding point ； To avoid introducing additional interference due to uneven ground potentials. ③The transmitter should be installed away from all magnetic sources, with no vibration allowed. ④When using a power supply, the transmitter and the secondary meter must use the same phase wire to avoid a 120-degree phase difference between the detection and feedback signals. , which prevents the instrument from functioning properly. ⑤The scale deposit on the inner wall of the transmitter tube should be cleaned regularly to prevent electrode short circuits and even the inability to measure flow rate. Always maintain the insulating lining inside the conduit of the gauge in good condition, to prevent corrosion caused by acids, alkalis, salts, etc., which could prevent the gauge from functioning properly. ⑥ Conduct periodic visual inspections of the gauge, check its surrounding environment, remove dust and debris, and ensure that no water or other substances get inside. ⑦Check whether the wiring is in good condition, and verify that there are no newly installed devices generating strong electromagnetic fields near the instruments, nor any new wires running across them. Common Faults and Solutions of Electromagnetic Flow Meters (1) Common Faults of Electromagnetic Flow Meters. The common faults that occur during the use of electromagnetic flow meters can be attributed either to damage to the components of the meter itself, or to issues resulting from improper selection, incorrect installation, environmental conditions, or characteristics of the fluid – problems such as fluctuating readings, reduced accuracy, or even damage to the meter. They can generally be divided into two types: faults that occur during installation and commissioning (commissioning phase faults) and faults that occur during normal operation (operational phase faults). ①Fault during the debugging period. Faults during the commissioning period generally occur during the installation and calibration of the instruments; once resolved, they usually do not reappear under the same conditions later on. Common faults during the commissioning period are usually caused by improper installation, environmental interference, and the effects of fluid properties. a. Pipeline systems and installation, etc. The fault is usually caused by an incorrect installation location of the electromagnetic flow meter; a common example is installing the sensor at the highest point of the pipeline network where gases tend to accumulate ； Or installed on a vertical pipe from top to bottom, evacuation may occur ； Or there is no back pressure behind the sensor, and the fluid flows directly into the atmosphere, resulting in a non-full condition within the measurement tube. b. Environmental aspects. Mainly pipeline stray current interference, strong electromagnetic wave interference in the environment, and magnetic field interference from large motors, etc. For interference caused by stray currents in pipelines, satisfactory results can usually be achieved by implementing proper separate grounding protection. However, in the presence of strong stray currents (such as those in electrolysis plants, where the peak value of the alternating voltage induced across the two electrodes can sometimes reach 1 V), additional measures are necessary, including insulating the flow sensors from the pipelines. Space electromagnetic wave interference generally enters through signal cables, and is usually protected by single-layer or multi-layer shielding. c. Fluid aspects. The presence of uniformly distributed tiny bubbles in the liquid being measured generally does not affect the proper operation of an electromagnetic flowmeter. However, as the bubbles grow larger, fluctuations occur in the instrument’s output signal. When the bubbles are large enough to cover the entire electrode surface, their passage over the electrodes can cause the electrode circuit to be momentarily interrupted, resulting in even greater fluctuations in the output signal. When an electromagnetic flowmeter driven by a low-frequency square wave is used to measure slurries with too high a solid content, slurry noise is also generated, causing fluctuations in the output signal. When measuring a mixed medium, if flow measurement is carried out before the mixture has become homogeneous, this will also cause fluctuations in the output signal. An inappropriate selection of electrode materials and the medium to be measured can also affect accurate measurements due to chemical reactions or polarization effects. The electrode material should be selected appropriately based on the instrument or relevant manuals. ②Operational failure. Operational faults are those that occur in electromagnetic flowmeters after they have been calibrated and are operating normally for some time. Common operational faults are generally caused by deposits on the inner wall of the flow sensor, lightning strikes, and changes in environmental conditions. a·Adhesive layer on the inner wall of the sensor. Since electromagnetic flowmeters are often used to measure dirty fluids, after operating for a period of time, an accumulation layer tends to form on the inner wall of the sensor, leading to malfunctions. These failures are often caused by the conductivity of the adhesion layer being too high or too low. If the attachment is an insulating layer, the electrode circuit will be open, preventing the instrument from functioning properly ； If the conductivity of the adhesive layer is significantly higher than that of the fluid, a short circuit will occur in the electrode circuit, and the instrument will not function properly. Therefore, the accumulated scale layer inside the measuring tube of the electromagnetic flowmeter should be removed in a timely manner. b. Lightning strike. Lightning strikes induce high voltages and surge currents in the instrument wiring, causing the instruments to be damaged. It is introduced mainly through the power cable, the excitation coil, or the flow signal line between the sensor and the converter, with the majority coming from the power cable in the control room. c. Changes in environmental conditions create interference sources. During debugging, when the environmental conditions are favorable (for example, there are no interference sources) and the flow meter operates properly, it is easy to overlook the installation conditions (such as inadequate grounding). Under such circumstances, once the environmental conditions change or new sources of interference arise during operation (such as welding on pipes near the flow meter or the installation of large transformers in the vicinity), it will disrupt the normal operation of the instrument, causing fluctuations in the output signal of the flow meter. (2) Troubleshooting of common faults in electromagnetic flowmeters ① No display on the instrument. When this fault occurs, first check whether the power supply is connected, verify that the power fuse is intact, and ensure that the supply voltage meets the requirements. If everything is normal, the converter should be sent to the manufacturer for repair. ②Excitation alarm. When this phenomenon occurs, it is necessary to check whether the excitation connections x and y are open-circuited, and to verify whether the resistance value of the excitation coil is normal, in order to determine whether there is a fault with the converter. ③Air traffic control alarm. When this problem occurs, it is necessary to check whether the fluid fills the sensor’s measurement tube and to verify that the signal connections are correct. Check whether the electrodes of the flow sensor are functioning properly. Short-circuit the converter’s signal input terminals a, b, and c with a wire; if the \"empty tube alarm\" message is dismissed at this point, it indicates that the converter is functioning properly. The issue may be due to a low conductivity of the fluid being measured, or incorrect settings for the empty tube threshold and range. ④The measured flow rate is inaccurate. When this occurs, it is necessary to check whether the fluid fills the sensor probe, whether the signal wires are properly connected, and to verify that the sensor coefficients and zero points are set correctly according to the sensor label or the factory calibration sheet. For more information, please visit the company’s official website at http://www.yb1518.com/. Please retain this link when reproducing the content! http://www.yb1518.com/UploadFiles/2012717174126829.jpg