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The advantages and disadvantages of electromagnetic flowmeters

There are more than 60 flow meters in the old style, each of which has its specific applicability and its limitations. According to the measurement object, there are two types of closed pipelines and open channels; according to the measurement purpose, it can be divided into total measurement and flow measurement. The meters are called the total meter and the flow meter.

In addition, according to the measurement principle can be divided into the following major categories:

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; and principle of using fluid momentum Target type; turbine type using angular momentum theorem; vortex type, vortex type using the principle of fluid oscillation; pitot tube type using volume difference of total static pressure, volumetric type, 堰, groove type, and the like.

Electrical Principles: Instruments used in such principles are electromagnetic, differential capacitive, inductive, strain resistant, etc.

Acoustic principle: ultrasonic measurement using the principle of acoustics for flow measurement. Acoustic (shock wave) and the like.

Thermal principle: The heat, direct thermal, indirect calorimetry, etc., which measure the flow using the thermal principle.

Optical principle: laser type, photoelectric type, etc. are instruments that belong to this principle.

Principles of atomic physics: nuclear magnetic resonance, nuclear radiation, etc. are instruments of this type.

Other principles: labeling principle (trace principle, NMR principle), related principles, etc.

In this paper, according to the most popular and widely used classification methods, the principle, characteristics, application and various aspects of the various flowmeters are explained in this case:

First, the electromagnetic flowmeter

1, advantages

(1) Electromagnetic flowmeters can be used to measure industrial conductive liquids or slurries.

(2) No pressure loss.

(3) The measuring range is large, and the diameter of the electromagnetic flow transmitter is from 2.5mm to 2.6m.

(4) The electromagnetic flowmeter measures the volumetric flow rate of the fluid under test. The measurement principle does not involve the effects of temperature, pressure, density and viscosity of the fluid.

2, disadvantages

(1) The application of electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of conductive medium, and can not measure the flow of non-conductive medium, such as gas and water for better heating. In addition, the lining needs to be considered under high temperature conditions.

(2) The electromagnetic flowmeter determines the volumetric flow rate under working conditions by measuring the speed of the conductive liquid. According to the measurement requirements, for liquid media, mass flow should be measured. The flow rate of the medium should be related to the density of the fluid. Different fluid media have different densities and vary with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is not appropriate to give only the volume flow at normal temperature.

(3) Installation and commissioning of electromagnetic flowmeters is more complicated than other flowmeters and requires stricter requirements. The transmitter and converter must be used together and cannot be used with two different types of instruments. When installing the transmitter, the selection from the installation site to the specific installation and commissioning must be carried out in strict accordance with the product specifications. The installation site must be free from vibration and strong magnetic fields. The transmitter and piping must be in good contact and well grounded during installation. The potential of the transmitter is equipotential to the fluid being measured. When using, the gas remaining in the measuring tube must be drained, otherwise it will cause a large measurement error.

(4) When the electromagnetic flowmeter is used to measure the viscous liquid with dirt, the sticky substance or sediment adheres to the inner wall or the electrode of the measuring tube, so that the output potential of the transmitter changes, which brings measurement error, and the dirt on the electrode reaches a certain level. Thickness may cause the meter to be unmeasured.

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