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Installation steps for plug-in electromagnetic flowmeters: 1. For plug-in electromagnetic flowmeters, it is required that the pipeline be horizontal, with at least 5DN of straight pipe section in front of the sensor and at least 3DN behind it. The flow control valve should be located 3DN downstream of the sensor. The pipeline should vibrate noticeably, and there should be no significant irregularities on its inner wall. 2. First, drill a hole with a diameter of Ф60-62mm directly above the measurement point on the pipe; the edges of this circular hole must be smooth, free of burrs or weld scars. 3. Unscrew the mounting piece from the sensor and weld it securely at the aforementioned opening; it is required that the lower end of the mounting piece be level with the inner surface of the pipe, and that no leaks occur. 4. Loosen the 3 locking screws of the sensor to pull out the detection rod and the detection head as a whole for subsequent installation. (Note: The user must not disconnect the connection between the detection head and the insertion rod.) 5. Wrap hemp thread or PTFE tape around the threaded end of the mounting piece, then tighten the ball valve along with its sealing mechanism onto it. 6. Slowly insert the testing rod from above again, tighten the lock nut slightly, press down on the insertion rod to ensure that L2 measured is the same as the recorded L2 value; the installation is then complete. Factors Affecting Measurement and Considerations for Selection I. Influence of Various Media on Measurement (1) Influence of flow velocity distribution: As known from fluid mechanics, when a liquid flows through a pipe, the flow velocities at different points across the pipe’s cross-section are not equal. However, whether in laminar or turbulent flow, after passing through a certain length of straight pipe, the flow velocity distribution becomes axially symmetric – with the highest velocity at the center of the pipe and zero at the pipe walls. The average flow velocity is V-. As long as the flow velocity distribution is symmetric with respect to the pipe’s central axis, the magnitude of the induced electromotive force generated at the electrodes is independent of the specific flow velocity distribution at various points; it depends only on the average flow velocity of the liquid being measured. Therefore, an axially symmetric flow velocity distribution is one of the operating conditions that must be satisfied by electromagnetic flowmeters with a uniform magnetic field. If the flow velocity distribution is asymmetric with respect to the tube’s central axis, although the total flow rate remains the same, the induced electromotive force near the electrodes is high; as a result, the measured signal is higher than the actual flow rate. Conversely, at a position 90° from the electrode, the small induced electromotive force results in a signal that is lower than the actual flow rate, leading to measurement errors. Therefore, to make the flow velocity distribution axisymmetric, it is necessary to add a straight pipe section in front of the flow meter. ⑵ The effect of the magnetic field’s edge effects on measurements: If it is assumed that the magnetic field remains uniform along the flow direction of the fluid, this actually implies that the magnetic field extends infinitely along the axis of the tube. In reality, however, the magnetic field in a flow meter has a finite length. Therefore, it is necessary to take into account the impact of the edge effects caused by a finite-length magnetic field on the measurements. Assuming the tube wall is insulating, the magnetic field near the electrodes is roughly uniform, while it gradually weakens at the ends, forming non-uniform edges that eventually drop to zero. As a result, the electric field E inside the liquid becomes non-uniform as well, which generates eddy currents. The secondary flux generated by eddy currents, in turn, alters the working flux in the edge areas of the magnetic field, further compromising its uniformity. At this point, the induced electromotive force measured at the electrode is different in magnitude from that in an infinitely long magnetic field, resulting in an error. If the tube wall is conductive, the edge effects of the magnetic field become more pronounced due to the short-circuiting effect of the conductive wall. This effect becomes even more significant as the electrical conductivity of the wall and its thickness change, thereby leading to an increase in the loss of induced electromotive force at the electrodes. For electromagnetic flowmeters, it is essential to insulate the pipe wall, so the wall is usually coated with an insulating layer. If the medium under test contains magnetic conductive materials, the edge effects of the magnetic field become more complex. The presence of magnetic conductive materials causes severe distortion of the magnetic field, resulting in nonlinear measurements. Therefore, for liquids containing liquid metal being measured, direct current excitation is generally used to reduce magnetic field edge effects. ⑶ Due to the influence of the conductivity of the medium being measured, the input impedance of the converter in plug-in electromagnetic flowmeters has been increased. When measuring conductive liquids, slight changes in the medium’s conductivity generally do not cause errors. However, for a given input impedance of the converter, there is a minimum value for the conductivity of the medium; it cannot be lower than this minimum value. It is also not allowed for the conductivity of the medium under test to be too high. For example, when the conductivity exceeds around 10-1 S/cm, the flow rate signal is reduced, altering the indicated value; that is, the indicated flow rate is lower than the actual flow rate. When the conductivity of the medium being measured is very high, the resistance of the external circuit is low; in this case, regardless of how high the input impedance of the converter is, the parallel combination will be determined by this external circuit for the liquid, thereby reducing the transmission accuracy between the transmitter and the converter. Therefore, for an electromagnetic flowmeter, there is a certain range within which the measurement is not affected by the conductivity of the medium; the conductivity of the medium being measured cannot be too high nor too low. If the conductivity of the medium is extremely high, large eddy currents will be generated in the magnetic field edge region, resulting in secondary fluxes that weaken and strengthen the magnetic fields on either side of the working magnetic field edge region. Therefore, media with high conductivity should not be excited using alternating current, but rather direct current. With the development of electronic technology and the increase in the input impedance of converters, it will surely be possible to lower the lower limit of the conductivity of the medium under test. III. Selection of flow sensors: Selection of electrode materials for electromagnetic flowmeters. If the electrode material is not properly matched to the medium being measured, chemical reactions or polarization effects can interfere with accurate measurement; therefore, the electrode material should be chosen based on the corrosiveness of the medium in question. Select the lining material for the electromagnetic flowmeter based on the corrosivity, wear resistance, and temperature of the medium being measured. Try to choose electromagnetic flowmeters with lightning protection features. IV. Installation of flow sensors 1. Requirements for the installation location. 1) When measuring mixed-phase fluids, select a location where phase separation will not occur; when measuring two-component liquids, avoid installing the device downstream where mixing has not yet been complete; when measuring chemical reaction pipelines, install it in the section where the reaction has fully taken place. ? 2) Try to avoid negative pressure forming inside the measurement tube. 3) Choose a location with minimal vibration, especially for integrated instruments. 4) Avoid having large motors, large transformers, etc., in the vicinity to prevent electromagnetic interference. 5) Locations where it is easy to achieve separate grounding for sensors. 6) Try to avoid areas with high concentrations of corrosive gases in the surrounding environment. 7) The ambient temperature should be within the range of -25 to 60°C, and the relative humidity should be between 10% and 90%; direct sunlight should be avoided as much as possible. 8) The liquid should have the conductivity required for measurement, and it is necessary that the conductivity distribution be roughly uniform. Therefore, the flow sensor should be installed away from areas where conductivity variations are likely to occur; for example, if chemicals are added near its upstream, the addition point should preferably be located downstream of the sensor. 2. Requirements for the length of the straight pipe sections: Insertion-type electromagnetic flowmeters have relatively low requirements regarding the straight pipe sections before and after them. In the case of 90° elbows, T-joints, concentric reducers, or fully open gate valves, it is sufficient to have a straight pipe section whose length is not more than 5 times the diameter from the electrode centerline, or from the connection surface at the sensor inlet; for valves with different degrees of opening, 1OD is required, while the straight pipe section downstream should be 3D in length. When measuring mixed liquids of different media, the distance between the mixing point and the flow meter should be at least 30D. 3. Installation position and flow direction: The sensor can be installed horizontally, vertically, or at an angle; there are no restrictions. However, it is best to install the device vertically for measuring solid-liquid two-phase fluids, with flow from bottom to top. This prevents severe localized wear on the lower part of the lining during horizontal installation, as well as issues such as solid phase precipitation at low flow rates. When installed horizontally, the electrode axis should be parallel to the horizon, in order to prevent insulation issues caused by occasional bubbles in the liquid brushing against and covering the electrode surface; this also helps to avoid the electrodes at the bottom from being covered by sediment. When installed vertically, the flow direction should be upward; this allows the heavier solid particles mixed in the fluid to sink when there is no flow or only a low flow, while the lighter fatty substances rise and move away from the sensor electrodes of the flow meter. 4. Grounding: The sensor must be grounded separately, with a grounding resistance of less than 100Ω. In principle, for separate types, grounding should be on the sensor side, while the converter’s grounding should be at the same grounding point. 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/201412269333291.jpg