Selection of electrodes and lining
Standard electrodes are used for media that do not produce non-staining electrodes such as crystals, agglomerates, and scales. Otherwise, a doctor blade electrode is used. In addition to the pure alkaline solution, the dosing solution (crystallization of boron and magnesium double salt), the washing liquid and other electromagnetic flowmeters that use the scraper electrode, the other uses the electromagnetic flowmeter of the standard electrode. Since the process pipes in the workshop are basically made of plastic insulation material, if the electromagnetic flowmeter with two electrodes is selected, the grounding ring must be configured to ensure the measurement accuracy. However, the common grounding ring is easy to corrode, and the corrosion-resistant titanium or 钽 grounding ring is high in cost, so the three-electrode electromagnetic flowmeter is selected to ensure measurement accuracy, reduce cost, and convenient installation and maintenance.
Flowmeter type selection
The types of electromagnetic flowmeters are divided into: integral type and split type. In Qinghai, the coldest temperature in winter is up to -30 °C. Many metered electromagnetic flowmeters are outdoors, and the environmental humidity of magnesium-lithium separation, pressure filtration and washing processes in lithium and boron systems is large. Exquisite, evaporation, conversion and other processes up to 90 °C. Therefore, the humidity of the high temperature, low temperature, high temperature fluid, vibration source and other working conditions select a split flow meter to effectively prevent the impact on the measuring components, to ensure measurement accuracy and the life of the electromagnetic flowmeter. However, it should be noted that the signal cable between the electromagnetic flowmeter sensor and the transmitter should not be too long, and the manufacturer-specific cable should be used, otherwise the measurement accuracy will be affected. The rest of the working conditions are more ideal.
Accuracy class and function According to the measurement requirements and the use occasions, the instrument accuracy level is selected to achieve economical efficiency. For example, in the case of trade settlement, product handover and energy measurement, the accuracy level should be higher, such as 1.0, 0.5, or higher; for process control, select different accuracy levels according to control requirements; It is to detect the process flow, no need to do precise control and measurement, you can choose a lower accuracy level, such as 1.5, 2.5, or even 4.0, then you can use a low-cost plug-in electromagnetic flowmeter.
Measuring medium flow rate, meter range and diameter When measuring general medium, the full flow of electromagnetic flowmeter can be selected within the range of 0.5-12m/s of measuring medium flow, and the range is wider. The meter specification (caliber) is not necessarily the same as the process pipeline. It should be determined whether the measured flow range is within the flow rate range. That is, when the pipeline flow rate is too low to meet the flow meter requirements or the measurement accuracy cannot be guaranteed at this flow rate, It is necessary to reduce the gauge diameter, thereby increasing the flow rate inside the tube and obtaining satisfactory measurement results.
Try to avoid ferromagnetic objects and equipment with strong electromagnetic fields to prevent the magnetic field from affecting the working magnetic field and flow signal of the sensor.
Should be installed in the dry and ventilated place, to avoid sun and rain, the ambient temperature should be -20 ~ +60 ° C, relative humidity is less than 85%.
There should be ample space around the flowmeter for easy testing and maintenance.
Measuring principle of electromagnetic flowmeter
The principle of electromagnetic flowmeter measurement is based on Faraday's law of electromagnetic induction. The measuring tube of the flow meter is a non-magnetic alloy short tube lined with an insulating material. The two electrodes are fixed to the measuring tube through the tube wall in the tube diameter direction. The electrode tip is substantially flush with the inner surface of the liner. When the exciting coil is excited by the bidirectional square wave pulse, a working magnetic field having a magnetic flux density B is generated in a direction perpendicular to the axis of the measuring tube. At this time, if the fluid having a certain conductivity passes through the measuring tube, the cutting magnetic line induces the electromotive force E. The electromotive force E is proportional to the product of the magnetic flux density B, the inner diameter D of the measuring tube and the average velocity V. The electromotive force E (flow signal) is detected by the electrode and sent to the converter through the cable. After the converter amplifies the flow signal, it can display the fluid flow, and can output signals such as pulse and analog current for flow control and regulation.