Electromagnetic flowmeter is a new type of flow measurement
instrument that developed rapidly with the development of electronic technology
in the 1960s. Its principle is developed based on Faraday's law of
electromagnetic induction. It is used to measure the volume flow of conductive
fluids in pipelines, including acids. , alkali, salt and other highly corrosive
liquids. Electromagnetic flowmeters are widely used in petroleum, chemical,
metallurgy, textile, food, pharmaceutical, paper and other industries as well
as environmental protection, municipal management, water conservancy
construction and other fields.
The main features of electromagnetic
flowmeters are:
The transmitter of the electromagnetic flowmeter has a simple
structure, with no moving parts and no throttling parts that hinder the flow of
fluid, so it will not cause any additional pressure loss when the fluid passes
through, and it will not cause wear, blockage, etc. It is especially suitable
for measuring liquid-solid two-phase fluids such as slurry with solid
particles, sewage, and various viscous slurries. Similarly, since there are no
moving parts in its structure, the electrodes can be made by attaching a
corrosion-resistant insulating lining and selecting corrosion-resistant
materials, which is often called an anti-corrosion electromagnetic flowmeter.
It has good corrosion resistance and can be used in Measurement of various
corrosive media.
The electromagnetic flowmeter is a volume flow measurement
instrument. During the measurement process, it is not affected by the
temperature of the measured medium. The influence of viscosity, density and
conductivity (within a certain range). Therefore, after being calibrated with
water, the electromagnetic flowmeter can be used to measure the flow of other
conductive liquids without additional corrections.
The measuring range of electromagnetic flowmeter is extremely wide,
and the measuring range ratio of the same electromagnetic flowmeter can reach
1:100. In addition, the electromagnetic flowmeter is only proportional to the
average flow velocity of the measured medium and has nothing to do with the
flow state (laminar flow or turbulent flow) under the axially symmetric
distribution.
The electromagnetic flowmeter has no mechanical inertia, is
sensitive in response, can measure instantaneous pulsating flow, and has good
linearity. Therefore, the measurement signal can be linearly converted directly
into a standard signal output using a converter, which can be indicated locally
or transmitted over a long distance.
Although the electromagnetic flowmeter has the above excellent
characteristics, it still has some shortcomings, mainly as follows:
1. The electromagnetic flowmeter can only
measure conductive liquids and cannot be used to measure gases, vapors and
liquids containing a large amount of gases.
2. Electromagnetic flowmeters cannot
currently be used to measure liquid media with very low conductivity. The
conductivity of the liquid medium to be measured cannot be less than 10-5
(S/cm), which is equivalent to the conductivity of distilled water. There is
nothing that can be done about petroleum products or organic solvents.
3. Since the insulating lining material of
the measuring tube is limited by temperature, current industrial
electromagnetic flowmeters cannot measure high-temperature and high-pressure
fluids.
4. The electromagnetic flowmeter is
affected by the flow velocity distribution. Under the condition of axially
symmetric distribution, the flow signal is proportional to the average flow
velocity. Therefore, there must be a certain length of straight pipe sections
before and after the electromagnetic flowmeter.
5. Electromagnetic flow meters are
susceptible to external electromagnetic interference.