Electromagnetic flowmeter properties and working principle

The working principle of electronic magnetic flow meter

Electromagnetic flowmeter is a kind of variable area flowmeter. The working principle of electromagnetic flowmeter is that in a vertical cone tube that expands from bottom to top, the gravity of the circular cross-section float is borne by hydrodynamic force, and the float can move in the cone. The tube rises and falls freely. It moves up and down under the action of flow rate and buoyancy, and after balancing with the weight of the float, it is transmitted to the dial to indicate the flow through magnetic coupling.

The electromagnetic flowmeter consists of two parts: the first part is a tapered tube that gradually expands from bottom to top; the second part is a rotor that is placed in the tapered tube and can move freely up and down along the center line of the tube.

Usually two methods are used to make the rotor move up and down on the center line of the conical tube without touching the tube wall: one is to install a guide mandrel in the center of the rotor to keep the rotor moving up and down on the center line of the conical tube. ; The other is that there are a series of inclined grooves on the edge of the rotor disc. When the fluid flows through the rotor from bottom to top, it bypasses the rotor while passing through the inclined groove to generate a reverse thrust, so that the rotor can continuously move around the center line. Rotation keeps the rotor from hitting the pipe wall during operation.

The characteristics of density flow meter

The rotor material of electromagnetic flowmeter can be made of stainless steel, aluminum, bronze, etc.

Electromagnetic flowmeters are the most commonly used flowmeters in industry and laboratories. It has the characteristics of simple structure, intuitive, small pressure loss, convenient maintenance and so on. The electromagnetic flowmeter is suitable for measuring small flow through the pipe diameter D<150mm, and can also measure the flow of corrosive medium.

When in use, the flowmeter must be installed on a vertical pipe section, and the fluid medium passes through the electromagnetic flowmeter from bottom to top.

Advantages and disadvantages of electromagnetic flow

Advantages:

1. The diameter of the electromagnetic flowmeter can range from several millimeters to several meters. At present, there are real-flow calibration equipment with a diameter of 3m in China, which lays the foundation for the application and development of electromagnetic flowmeters.

2. The sensor structure of the electromagnetic flowmeter is simple, there are no moving parts in the measuring tube, and there is no throttling part that hinders the flow of the fluid. It is one of the flow meters with the lowest operating energy consumption in the flowmeter.

3. The electromagnetic flowmeter can measure the flow of dirty medium, corrosive medium and suspended liquid-solid two-phase flow. Only the measuring tube lining and electrode of the electromagnetic flowmeter are in contact with the measured medium, and the material can be selected according to the properties of the measured fluid.

e.g:

(1) The electromagnetic flowmeter is lined with polytrifluoroethylene or polytetrafluoroethylene, which can measure various acids, alkalis, salts and other corrosive media.

(2) The electromagnetic flowmeter adopts wear-resistant rubber lining, which is especially suitable for measuring liquid-solid two-phase flows such as ore pulp and cement slurry with solid particles and large wear, as well as various suspended liquids such as fiber liquid and pulp. .

4. The range of the electromagnetic flowmeter is extremely wide, and its measurement range can reach 100:1, and even the operable flow range of 1000:1.

5. The electromagnetic flowmeter has no mechanical inertia and has a sensitive response. It can measure the instantaneous pulsating flow. The intelligent electromagnetic flowmeter can measure the flow in both positive and negative directions.

6. The electromagnetic flowmeter is not affected by the temperature, viscosity, density and conductivity of the measured medium (within a certain range) during the measurement process. Electromagnetic flowmeter is a volume flow measuring instrument, which can be used to measure the flow of other conductive liquids only after being calibrated by water.

Disadvantages:

1. At present, electromagnetic flowmeters cannot be used to measure liquid media with very low conductivity, such as the flow of petroleum products or organic solvents.

2. The electromagnetic flowmeter cannot be used to measure the flow of gas, steam and liquid containing a large amount of gas at present.

3. The electromagnetic flowmeter installation and debugging requirements are strict.

(1) Electromagnetic flowmeter sensors and converters must be in one-to-one correspondence, and products of different models cannot be used interchangeably.

(2) The electromagnetic flowmeter installation must comply with the installation specifications.

4. When the electromagnetic flowmeter measures dirty or viscous media, the medium will adhere to the inner wall or the electrode (the scraper electrode can remove the dirt covering the electrode), and the electromagnetic flowmeter will bring errors as the thickness of the dirt increases, and even Can not work normally.

5. Due to scaling or wear of the inner aperture of the electromagnetic flowmeter, the original flow value of the flowmeter will be changed, resulting in measurement errors.

6. To improve the measurement accuracy and anti-interference ability of electromagnetic flowmeters, high-performance converters need to be selected, and the cost increases a lot.

7. The electromagnetic flowmeter is easily affected by external strong electromagnetic signals.