Choice of caliber
The choice of the diameter of the electromagnetic flowmeter is not necessarily the same as the diameter of the pipe, and should be determined by the flow rate and flow rate. However, as the chemical raw materials and intermediate liquid of Salt Lake, the viscosity is large and the flow rate is low (generally 2.0 to 4.0 m/s). The electromagnetic flowmeter is used on such a pipe, and the diameter of the sensor is the same as the diameter of the pipe. If the flow rate is lower than 1.0m/s, an electromagnetic flowmeter of appropriate flow rate can be selected to ensure measurement accuracy and relatively reduce investment.
Selection of flow rate and range
Basically, they are anti-corrosion plastic pipes, and considering the lining of the flow meter, the flow rate is generally controlled at 2m/s. For some materials that are easy to crystallize (such as sodium carbonate solution, compounding liquid: crystallized mainly boron and magnesium double salt), the flow rate is increased to 3.0 to 4.0 m/s by taking measures. The flow rate will increase the flow noise, and the vibration of the pipeline will affect the measurement accuracy. Under the condition that the electromagnetic flowmeter is installed, the shock absorber should be installed before and after. The full scale of the meter is greater than the expected maximum flow value, which is typically 1.2 times the estimated maximum flow. The normal measurement flow is greater than 50% of the full scale of the meter to ensure a certain measurement accuracy.
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.
Principle analysis of various types of flowmeters
(1) Principles of mechanics: Instruments belonging to such principles have differential pressure and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law; The target type of the momentum principle; the turbine type using the angular momentum theorem; the vortex type using the principle of fluid oscillation, the vortex type; the pitot tube type using the total static pressure difference; the volumetric type, the enthalpy, the trough type, and the like.
(2) Electrical principle: The instruments used for such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.
(3) Acoustic principle: Ultrasonic type, acoustic type (shock wave type), etc. are used for flow measurement using the acoustic principle.
(4) Thermal principle: The heat, direct thermal, indirect calorimetry, etc., which measure the flow using the thermal principle.
(5) Optical principle: laser type, photoelectric type, etc. are instruments belonging to such principles.
(6) Originally based on physical principles: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.
(7) Other principles: Marking principle (trace principle, NMR principle), related principles, etc.