Electromagnetic flowmeter is an instrument for measuring conductive liquid made according to Faraday’s law of electromagnetic induction. Electromagnetic flowmeter consists of three parts: sensor, converter, and cable connection line, all of which are indispensable. If the cable connection is short, install it in the flowmeter housing.The electromagnetic flowmeter has a series of excellent characteristics, which can solve the problems that other flowmeters are not easy to apply, such as the measurement of dirty flow and corrosive flow.Advantages:The measuring channel is a smooth straight pipe, which will not be blocked. It is suitable for measuring liquid-solid two-phase fluids containing solid particles, such as pulp, mud, sewage, etc.;No pressure loss caused by flow detection, and good energy-saving effect;The measured volume flow is actually not significantly affected by changes in fluid density, viscosity, temperature, pressure and conductivity;Large flow range and wide caliber range;Corrosive fluids can be used.Disadvantages: cannot measure liquids with very low conductivity, such as petroleum products; cannot measure gases, steam and liquids with larger bubbles; cannot be used for higher temperatures.Commonly used in chemical plants are electromagnetic flowmeter joint venture or imported brands such as E+H (Endress+Hauser), KROHNE (Cologne), ABB, Yokogawa, Siemens and so on. Domestic brands of electromagnetic flowmeters include Huikeda Instruments, Chuanyi and so on.Installation requirements of electromagnetic flowmeterChoice of installation siteIn order to make the electromagnetic flowmeter work stable and reliable, the following requirements should be paid attention to when choosing the installation location:1. Try to avoid ferromagnetic objects and equipment with strong electromagnetic fields (large motors, large transformers, etc.) to prevent the magnetic field from affecting the working magnetic field and flow signal of the sensor.2. It should be installed in a dry and ventilated place as far as possible, avoiding sun and rain. The ambient temperature should be -20～＋60℃, and the relative humidity should be less than 85%.3. There should be ample space around the flowmeter for easy installation and maintenance.Eleven installation suggestions1. Ensure full pipe installationThe measuring tube of the electromagnetic flowmeter must be full, and there must be no partial tube state. If the pipeline is not full or the outlet is vented, the sensor should be installed on a siphon.Avoid installing on the upstream of the downward pipeline Avoid high points of the pipeline, which tend to accumulate bubbles2. Horizontal and vertical installationThe sensor can be installed horizontally and vertically, but it should be ensured to avoid the influence of deposits and bubbles on the measuring electrode, and it is better to keep the electrode axis horizontal. When installing on a horizontal pipeline, the two measuring electrodes should not be directly above and directly below the pipeline. When installed vertically, the fluid should flow from bottom to top. The inlet straight pipe should be larger than 5D, and the outlet straight pipe should be larger than 2D. If there are specific installation requirements, it should be installed according to the electromagnetic flowmeter manual. The plug-in inlet straight pipe section should be ≥20D, and the outlet straight pipe section ≥7D (D is the nominal diameter of the sensor.3. Installation when the outlet is vented When the outlet is vented, the sensor should not be installed where the pipeline is vented, but should be installed at a lower place. When the sensor is installed below the pipeline, it should be ensured that the sensor is filled with liquid and that there is no empty pipe state.4 Series installation and parallel installation If several sensors need to be connected in series on the same pipe in sequence, the distance between each sensor should be at least the length of 2 sensors. If two or more sensors are installed in parallel with each other, the distance between the sensors must be greater than 1m.5 Installation between elbows, valves and pumps To ensure the stability of the measurement, straight pipe sections should be set before and after the sensor, the length of which is given in the figure below. If this is not possible, a current stabilizer should be used or the cross-sectional area of the measuring point should be reduced. Installation plus bypass pipeline The pipeline where the flowmeter is installed should have a valve that can cut off the medium in the pipeline to facilitate daily maintenance and maintenance. When the process does not tolerate flow interruption. A bypass pipe can be added to the pipe where the flowmeter is installed.7. Install according to the calibration direction. When the flowmeter sensor has a clear flow mark, it should be installed according to the calibration direction.8 Wire inlet, cable and wire pipe flow meter wire inlet, cable and wire pipe should be bent downwards and open at the lowest point to avoid water ingress and short circuit.9. Welding flange When installing the flowmeter, the flange should be welded first, and then the flowmeter should be installed. It is not possible to directly weld the flange with the flowmeter sensor directly to prevent the welding slag from burning the lining.10. The distance between the converter and the sensor The signal wire between the converter and the sensor cannot be greater than 50m, and the signal wire must be sheathed with galvanized pipe.11. Sensor grounding measures: The flow signal generated by the sensor is very small, only a few millivolts at full scale, so the sensor should be well grounded. There are two aspects to the grounding requirements of electromagnetic flowmeters: Analyze from the working principle of electromagnetic flowmeters and the loop of flow induction signal current, the grounding terminals of sensors and converters must be at the same potential as the measured medium.Ground, take the earth as zero potential to reduce external interference.Under normal circumstances, process pipelines are all metal pipes, and they are all grounded. This requirement is easy to meet. However, in the case of large external electromagnetic field interference, the electromagnetic flowmeter should be equipped with a grounding device. The grounding wire should be a multi-stranded copper wire with a cross-section greater than 5mm2. The grounding wire of the sensor must not be connected to the common ground wire of the motor or other equipment. To avoid the influence of leakage current. The grounding resistance should be less than 10Ω.
Post time: 21-09-21