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Electromagnetic flowmeters are highly favored by enterprises in industries such as petrochemicals and chemicals due to their advantages of no pressure loss, high precision, and reasonable price, and they play an important role in flow measurement. However, in practical applications, due to improper operation, unsuitable selection of equipment, and unscientific installation, measurement errors are difficult to avoid, causing trouble for users. Therefore, those working in the field of instruments should pay attention to various factors that cause errors in electromagnetic flowmeters. Generally speaking, the main factors causing errors in electromagnetic flowmeters can be divided into three categories: improper selection, the influence of the fluid being measured, and interference. I. The flow velocity range that can be measured by an electromagnetic flowmeter for the liquid to be tested is generally 0.5–10 m/s, with the optimal flow velocity range being 1.5–3 m/s. In actual use, the inner diameter of the measurement tube should be determined based on the flow rate to be measured and the flow velocity range that the electromagnetic flowmeter can measure. II. Selection of electrode and lining materials: The electrode and lining materials come into direct contact with the liquid to be tested. These materials should be selected based on the properties of the liquid (such as corrosivity and abrasiveness) as well as the operating temperature. If the wrong materials are chosen, issues such as rapid adhesion, corrosion, scaling, wear, and deformation of the lining may occur, leading to measurement errors. III. Excitation stability: The excitation methods for electromagnetic flowmeters include DC excitation, AC sine wave excitation, and dual-frequency rectangular wave excitation. DC excitation can lead to electrode polarization and DC interference issues, while AC sine wave excitation may cause fluctuations in the zero point. Dual-frequency rectangular wave excitation combines the excellent zero-point stability of low-frequency rectangular wave excitation with the strong ability to suppress fluid-induced noise from high-frequency rectangular wave excitation, making it an ideal excitation method. In practical applications, it is necessary to ensure stability in power supply voltage and frequency as much as possible, in order to maintain a constant magnetic field strength and reduce measurement errors caused by variations in magnetic field strength. IV. Electromagnetic flowmeters for measuring mixed-phase fluids: When using an electromagnetic flowmeter to measure the flow rate of liquid-solid mixed-phase fluids (such as water containing sediment), errors in measurement can occur if a flowmeter calibrated for single-phase liquids is used. In such cases, it is necessary to install the sensor in a straight pipe section where no separation between the liquid and solid phases takes place. Effect of the liquid to be tested: I. Sharp changes in the conductivity of the liquid to be tested. When the conductivity of the liquid is high, it causes significant fluctuations in the displayed values; if the problem is severe, it becomes difficult for the control system to function properly ； When the conductivity of the liquid to be tested is too low, it is difficult for the electrodes to produce a proper output; if the conductivity falls below the minimum threshold during operation, then the electromagnetic flowmeter will have difficulty functioning properly. In response to these situations, first of all, it is necessary to base the selection of electromagnetic flowmeter types on actual needs, taking into account relevant standards and requirements ； Secondly, install reactors or straight pipe sections to ensure thorough mixing of the materials and facilitate the smooth progress of chemical reactions ； Once again, the selection of flowmeter type is to be carried out anew. II. Bubbles in the liquid to be tested or a non-full tube: Regarding bubbles, they mainly arise from gases dissolved in the liquid turning into free bubbles, as well as bubbles drawn in from the outside. A flow rate containing a large volume of bubbles can affect the accuracy of the measurement. If the bubble diameter is too large, even exceeding the diameter of the electrode, instability will occur during the measurement process, and fluctuations are inevitable. To address this situation, first, a gas collector can be installed on the electromagnetic flowmeter, along with periodic exhaust operations ； Secondly, replace the installation location appropriately ； Once again, install the vertical pipe on the electromagnetic flowmeter to ensure a bottom-up orientation ； Fourth, when installing the sensor, avoid placing it too close to the exhaust outlet ； Fifth, install the sensor at the control valve, upstream of it, or downstream of the pump. III. If the conductivity of the liquid to be tested is too low, its reduced conductivity increases the output impedance of the electrodes. The load effect caused by the input impedance of the converter leads to measurement errors. If the actual conductivity is below the lower limit value, the instrument cannot function properly, and the displayed values will fluctuate. Solution: Choose other electromagnetic flowmeters with low conductivity that meet the requirements, such as electromagnetic flowmeters ； Other principle-based flowmeters, such as orifice plates, can be used. IV. Measurement of the asymmetric state of liquids: In measurements where the liquid under examination is asymmetric, there are two main types of flow patterns: one is a single vortex flow ； The other is a straight-flow along the pipeline axis, with the volumetric flow rate of the liquid being the integral of the pipe cross-section. To address the issue of insufficient straight pipe sections upstream, a flow regulator can be used for adjustment ； Secondly, ensure that the inner diameter of the pipeline within a reasonable range upstream and downstream has the same value as the inner diameter of the flow meter ； Once again, ensure there is sufficient straight pipe section upstream. V. There is a layer inside the measuring tube; electromagnetic flowmeters are often used to measure unclean fluids. Non-clean fluids contain various substances such as precipitates, which contaminate the surface of the electromagnetic flowmeter electrodes or the inside of the pipes, leading to errors in the measurement results. To address this situation, first, clean the electromagnetic flowmeter regularly ； Secondly, increase the flow rate appropriately and keep it at 4 m/s ； Once again, linings made of materials such as polytetrafluoroethylene are used. 1. The cable connecting the spatial electromagnetic interference converter and the sensor is relatively long; in strong electromagnetic environments, it is prone to interference, which can cause nonlinearities in the instrument’s measurement values, making it difficult for the readings to be displayed properly. To address this situation, first, shielding measures should be implemented: cables can be introduced separately through grounded steel pipes, and shielded cables that meet the required standards should be used ； Secondly, reasonably shorten the cable length ； Once again, stay at a distance from strong magnetic fields. II. Issues with connection cables: The essence of using electromagnetic flowmeters lies in utilizing specific cables to connect the converter to the sensor, thereby forming a complete system; therefore, factors such as the cross-sectional area of the conductors, capacitance, and the cable layout can have adverse effects. To address this situation, first, it is necessary to ensure that the cable model meets the requirements in order to achieve an effective connection at the ends, thereby preventing the occurrence of intermediate joints ； Secondly, the length range should be controlled; generally, the shorter it is, the better. Thirdly, regarding the grounding issue, since the output signal of the sensor is very small, usually only a few millivolts, to improve resistance to interference, the sensor’s zero potential must be grounded reliably separately, and the grounding point for the sensor’s output signal should be electrically connected to the fluid being measured. The grounding resistance of the sensor should be less than 10Ω. When the pipeline connecting the sensor is coated with an insulating layer or is made of a non-metallic material, grounding rings should be installed on both sides of the sensor and connected to ground reliably, so as to ground the fluid and make its potential equal to the ground potential. IV. Vibration at the installation points of the symmetric points of the electrodes and excitation coils The excitation coils and electrodes of an electromagnetic flowmeter must be symmetrical; if they are not, deviations will occur during production, making it difficult to ensure accurate measurement results. Furthermore, the installation location must meet high vibration resistance standards; otherwise, the accuracy of the measurement values cannot be guaranteed, and it may even cause the instruments to malfunction. It relies on grounding, and the ground point of the sensor’s output signal should be electrically connected to the fluid being measured. The grounding resistance of the sensor should be less than 10Ω. When the pipeline connecting the sensor is coated with an insulating layer or is made of a non-metallic material, grounding rings should be installed on both sides of the sensor and connected to ground reliably, so as to ground the fluid and make its potential equal to the ground potential. For more information, please visit the company’s official website at http://www.yb1518.com/. Please keep this link when reproducing the content!