Instruments that measure fluid flow are collectively referred to as flow meters or flow meters. The flowmeter is one of the important instruments in industrial measurement. With the development of industrial production, the accuracy and range of flow measurement requirements are getting higher and higher, and the flow measurement technology is changing with each passing day. Various types of flow meters have been introduced to suit various applications. More than 100 flow meters have been put into use. From different perspectives, flow meters have different classification methods. There are two commonly used classification methods. One is to classify according to the measurement principle adopted by the flowmeter: the second is to classify according to the structural principle of the flowmeter.
Sort by measurement principle
a. Mechanical principle:
Instruments belonging to such principles have differential pressure type, rotor type using Bernoulli's theorem;
Impulse type using the momentum theorem, movable tube type;
Direct mass equation using Newton's second law;
a target using the principle of fluid momentum;
Turbine using the angular momentum theorem;
Vortex type using vortex principle of fluid oscillation;
Use the total static pressure difference of the pitot tube type as well as volumetric and sputum, trough and so on.
b. Electrical principle:
Electromagnetic,
Differential capacitor type,
Inductive,
Strain resistance type, etc.
c. Acoustic principle:
Ultrasonic.
d. Thermal principles:
Thermal type,
Direct calorimetry,
Indirect calorimetry and so on.
The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring conduit, an electrode, a casing, a lining, and a converter.
Magnetic circuit system: its role is to produce a uniform DC or AC magnetic field. The DC magnetic circuit is realized by a permanent magnet, which has the advantages of simple structure and less interference by the alternating magnetic field, but it is easy to polarize the electrolyte liquid in the measuring duct, so that the positive electrode is surrounded by negative ions, and the negative electrode is positive ion Surrounding, that is, the polarization phenomenon of the electrode, and causing an increase in internal resistance between the two electrodes, thus seriously affecting the normal operation of the meter. When the diameter of the pipe is large, the permanent magnets are correspondingly large, bulky and uneconomical, so the electromagnetic flowmeter generally adopts an alternating magnetic field and is generated by the excitation of a 50HZ power frequency power source.
Measuring catheter: its function is to let the conductive liquid to be tested pass. In order to make the magnetic flux diverted or short-circuited when the magnetic flux passes through the measuring catheter, the measuring catheter must be made of non-magnetic, low electrical conductivity, low thermal conductivity and mechanical strength. Non-magnetic stainless steel, FRP, high strength can be used. Plastic, aluminum, etc.
Application of electromagnetic flowmeter
Because electromagnetic flowmeter has its unique advantages, it is widely used in chemical, chemical fiber, food, paper, sugar, water supply and drainage, environmental protection, water conservancy, steel, petroleum, pharmaceutical and other industrial fields. Various acid and alkali salt solutions, mud, pulp, pulp, coal water slurry, corn syrup, fiber pulp, lime slurry, water supply and drainage, brine, hydrogen peroxide, beer, wort, various beverages, black liquor, green liquor, etc. The volumetric flow of the medium.
The main technical parameters
Nominal diameter series DN (mm)
Pipeline PTFE lining:
10,15,20,25,32,40,50,65,80,100,
125,150,200,250,300,350,400,
450,500,600
Pipeline rubber lining:
40,50,65,80,100,125,150,200,250,
300,350,400,500,600,800,1000,
1200
Special specifications can be customized
Flow direction: current output
Positive, negative, net flow
Range ratio: 150:1
Repeatability error: ±0.1 of the measured value
Accuracy level: pipeline type: 0.5 level, 1.0 level
Measured medium temperature
Ordinary rubber lining: -20 ~ +60 ° C
High temperature rubber lining: -20 ~ +90 ° C
PTFE lining: -30 ~ +100 ° C
High temperature PTFE lining: -30 ~ +180 ° C
Rated operating voltage
Pipe type: DN6-DN100≤1.6Mpa, DN125-DN225≤1.0Mpa high pressure can be customized
Conductivity range:
Conductivity of the measured fluid ≥ 5us / cm (integrated)
Most water-based media have a conductivity of 200-800 us/cm, and electromagnetic flow meters can be used to measure the flow rate.
Load resistance: 0 ~ 10mA, 0 ~ 1.5kΩ
4 to 20 mA, 0 to 750 Ω
Digital frequency output
The upper limit of the output frequency can be set to open the bidirectional output of the open collector of the transistor with optical isolation from 1 to 5000HZ. External ≤35V, the maximum current of the collector is 25mA when conducting
Power supply
85～265V, 45～63HZ
Straight pipe length
Pipeline type: upstream ≥5DN, downstream ≥2DN
Connection method
The flowmeter and the pipe are flanged, and the flange connection size should meet the requirements of GB11988.
Explosion-proof mark: mdllBT4
Ambient temperature: -10 ° C ~ +55 ° C
Relative temperature: 5% to 90%
Total power consumption: less than 15W