What is flow meter?
Flowmeter is an instrumentation device mostly used to measure the flow of fluids in pipes or open channels. Flow meter is an important part of measurement science and technology. Flow meters are widely used in various fields such as national defense construction, industrial and agricultural production, scientific research, foreign trade, and people's lives. If there is no flow measurement, then the industry will not be able to produce normally, and it will not be able to guarantee the trade between the industries. In the chemical industry, inaccurate flow measurement will cause chemical components to fail to meet the standard requirements, and product quality cannot be guaranteed.
In more serious cases, it may lead to production safety accidents. In industrial production, it is very important to measure and adjust the flow of liquid, gas, steam and other media. The accuracy of flow measurement is of great significance to industrial production. With the continuous development of science and technology, the accuracy of flow measurement in industrial applications has become an important factor to ensure safe operation
Flow meter types are divided according to the principle: volumetric flowmeter, differential pressure flowmeter, rotameter flowmeter, turbine flowmeter, Magnetic type flow meter, vortex flowmeter, mass flowmeter, etc.
Magnetic type flow meter History
Magnetic type flow meter is a kind of instrument device that can measure the volume flow of conductive liquid, which is made by the principle of Faraday's law of electromagnetic induction. In the early 1950s, the electromagnetic flowmeter realized industrial application. In the late 1970s, the low-frequency rectangular wave excitation replaced the power frequency AC excitation method used in the early stage. In recent years, magnetic flowmeters have been widely used as waste water flow meter or drinking water flow meter in water supply and drainage projects, slurry or pulp flow meter in the paper industry, Strong erosive liquid such as acid flow meter in chemical industry and blast furnace cooling water control and monitoring in iron and steel industry, pharmaceutical industry, food industry, biological engineering and other places with hygienic flow measurement requirements, for example acid flow meter, sanitary magnetic type flow meters, chemical flow meters. , etc.
Principle of Magnetic type flow meter
The measurement principle is based on Faraday's law of electromagnetic induction. That is: when the conductive liquid moves in the magnetic field to cut the magnetic field line, the conductor generates an induced electromotive force, and the induced electromotive force E is:
E = KBVD (1)
In the formula:
K is the instrument constant;
B is the magnetic induction intensity;
V is the average flow velocity in the measuring tube section;
D is the inner diameter of the measuring tube.
When the inductive flow meter measures the flow, a magnetic field is generated when the fluid flows perpendicular to the flow direction, and the flow of the conductive liquid induces a voltage proportional to the average flow rate (that is, the volume flow), and the induced voltage signal passes through two liquids. The electrodes in direct contact are detected and sent to the signal amplifier through a special signal cable, and finally converted into a unified output signal.
Magnetic Type Flow Meter Technical Specifications
Magnetic flow meter accuracy 0.2%- 0.5% ;
Magmeter flow sensor size: 1/2”, 3/4”, DN25, dial 40mm, 2inch magnetic flow meter. 3inch, DN100, 4 Inch electromagnetic flow meter, 5” magmeter, 6”, DN200, 8”, 300mm, magnetic flow meter, max can be made into 2000mm magnetic flow meter.
Fluids can be made: Liquid with conductivity over 5u/cm, normal measurement liquid include water, portable water, drinking water, waste water, sewage, chemical , acid ,HCL .,etc;
Pressure rating for magnetic flow meter: PN16,PN25,PN40, ANSI 150LB,ANSI 300LB,JIS 10K, 20K.,etc ;
Flow velocity for inductive flow meter: 0.5~10 m/s ;
Forward or reverse flow measurement, it is bi-direction flow meter;
Electrodes Material: SUS 316L, Hastelloy C , Hastelloy B ,tantalum, titanium, tungsten carbide, Platinum electrode;
Liner material: Teflon, PFA,rubber.,etc
Protection level: IP65,IP68;
Housing material: standard carbon steel, option with stainless steel 304 or 316;
Digital magnetic flow meter output: pulse , frequency or current 4-20Ma;
Communication: RS485 MODBUS, HART or PROFIBUS-DP
Process connection: Flanged ends or thread or tri-clamp or wafer connection;
Magnetic type flow meter Advantages
(1) The electro magnetic flow meter measurement is not affected by fluid density, viscosity, temperature, pressure and other working conditions;
(2) There is no throttling element in the measuring pipe, it is full bore flowmeter,, so when the liquid flows through, magnetic water meter will not cause pressure loss, and the requirements for straight pipe sections are relatively low compared with other types of flowmeters;
(3) mag meter flow meter has good corrosion resistance and wear resistance;
(4) The power consumption of magnetic inductive flow sensor is relatively low compared to other forms of flowmeters, the zero point is stable, and the accuracy is high;
(5) Magnetic inductive flow sensor has various installation forms can be easily selected by users, such as: integrated type mag meter, remote display type mag flow meters, and wall mount magnetic flow transmitters;
(6) The magnetic inductive flow sensor can measure bidirectionally,it is bi-directional flow meter, can display forward and reverse flow, and has a variety of output options, such as: current, pulse, digital communication, HART,PRODIBUS,MODBUS etc.
Disadvantages of Magnetic type flow meter
(1) Mag meter flow meter is impossible to measure gas, steam and medium containing a large amount of gas;
(2) Magnetic inductive flow sensor is basically impossible to measure liquid media with very low conductivity or non-conductivity, mag meter cannot be used to measure oil or diesel;
(3) Magnetic inductive flow meter will be affected by the surrounding strong magnetic field.
Selection of Magnetic type flow meter
1. Electrodes of magnetic flow sensor
In general, the standard electrodes are stainless steel 316L,they can be used for the medium that does not crystallize and contaminate the electrode; if the medium is corrosive, for example acid flow meters , it should be selected according to the corrosion medium to be measured. For example for HCL flow meter, hypochlorous acid flowmeter, sulfuric acid flow meter, we normally choose tantalum electrodes, for sea water flow meter, ferric chloride flow meter or caustic soda flowmeter we normally go for Titanium electrodes, industrial water flow meter, raw water, sewage, sewage, dilute acid, dilute alkali and other weakly corrosive acids, bases, and salts are recommended to use 316L material; seawater, salt water, weak acid, and weak base are recommended to use Hastelloy material; boiling point The strong corrosiveness of hydrochloric acid, nitric acid and sulfuric acid is recommended to use tantalum material.
2. Lining of magnetic flow sensor
Magnetic flow meter liner should be selected according to the corrosiveness of the measured medium, the wear characteristics of the medium and the operating temperature range of the medium. For example: -40 ~ 180 ℃, strong corrosive medium such as acid and alkali flow meter, hygienic medium is recommended to use Teflon,PFA material. -5 ~ 80 ℃, general water, sewage water flow meter, mud, pulp, it is recommended to use neoprene rubber material.
3. Requirements for enclosure protection level of magnetic type flow meter
According to the national standard GB 4208-2017 and the IEC standard of the International Electrotechnical Commission (IEC 529-76), the enclosure protection level is:
IPXX, the first representative is the dustproof level. Considering the harsh environment and uncertain factors in industrial production, we basically choose IP6X in industrial use. The 6 number represents complete protection from foreign objects and dust. Therefore, we basically choose IP65\IP66\IP67\IP68 for the protection level. In the industry, we basically choose IP65 and IP68. IP68 magnetic flow sensor is used which installed in the well or humid environment.
4. Grounding Ring
Ordinary grounding ring, protective grounding ring, used to protect PTFE flanging from damage and necked grounding ring, suitable for abrasive media, protect end lining, prolong sensor life (it is recommended to order and calibrate with the instrument, otherwise it may affect the accuracy ), grounding ring material: stainless steel, Hastelloy, tantalum, etc.
5. Installation method
Integral display magnetic type flow meter or remote display magnetic flow meter
6. Power Selection
220 VAC or 24 VDC or battery powered magnetic type flow meter;
7. Explosion-proof rating
Explosion proof type Exd IICT6 or non-explosion proof type;
To sum up, the key to the correct selection of magnetic type flow meter in the industry and to ensure long-term and reliable application is to confirm the design parameters, so as to ensure that the electromagnetic flowmeter is accurate and reliable during the selection, and strictly implemented after arrival. Acceptance criteria, installation and construction precautions are strictly in accordance with the magmeter manufacturer's instructions. It is believed that the electromagnetic type flowmeter will show accurate and reliable characteristics in long-term industrial applications in the future.