The electromagnetic flowmeter is a flowmeter that performs flow measurement according to Faraday’s law of electromagnetic induction. The advantage of the electromagnetic flowmeter is that the pressure loss is extremely small and the measurable flow range is large. The ratio of the maximum flow rate to the minimum flow rate is generally above 40:1. The applicable industrial pipe diameter range is wide, up to 3m. The output signal is linear with the measured flow rate, and the accuracy is high. It can measure the conductivity ≥5μs/cm Fluid flow of acid, alkali, salt solution, water, sewage, corrosive liquid and mud, mineral pulp, paper pulp, etc. But it cannot measure the flow of gas, steam, and pure water.

1. What Is The Difference Between Mass
Flow Meter And Magnetic Flow Meter?
The working theory is different
Electromagnetic flowmeter working theory
The electromagnetic flowmeter is a flowmeter that performs flow
measurement according to Faraday’s law of electromagnetic induction.
The advantage of the electromagnetic flowmeter is that the pressure loss
is extremely small and the measurable flow range is large. The ratio of
the maximum flow rate to the minimum flow rate is generally above 40:1.
The applicable industrial pipe diameter range is wide, up to 3m. The
output signal is linear with the measured flow rate, and the accuracy is
high. It can measure the conductivity ≥5μs/cm Fluid flow of acid, alkali,
salt solution, water, sewage, corrosive liquid and mud, mineral pulp,
paper pulp, etc. But it cannot measure the flow of gas, steam, and pure
water.
When a conductor cuts the lines of force in a magnetic field, an induced
electric potential will be generated in the conductor. The magnitude of the
induced electric potential is proportional to the effective length of the
conductor in the magnetic field and the speed at which the conductor
moves in the magnetic field perpendicular to the direction of the magnetic

2. field. In the same way, when the conductive fluid flows in the vertical
direction in the magnetic field and cuts the magnetic induction force lines,
it will also generate an induced electric potential on the electrodes on
both sides of the pipe.
Mass flow meter working theory
The mass flow meter adopts the heat-sensitive measurement to measure
the flow rate by the molecular mass taken away by the split molecules.
Because the heat-sensitive measurement is used, the gas temperature and
pressure changes will not affect the measurement result. The mass flow
meter is a relatively accurate, fast, reliable, efficient, stable, and flexible
flow measurement instrument, which will be more widely used in
petroleum processing, chemical industry, and other fields. It is believed
that it will show great potential in promoting flow measurement.
The mass flow meter cannot control the flow, it can only detect the mass
flow of liquid or gas, and output the flow value through analog voltage,
current or serial communication. However, the mass flow controller is an
instrument that can detect and control at the same time.
In addition to the measurement part, the mass flow controller itself also
has an electromagnetic regulating valve or piezoelectric valve, so that the
mass flow control itself constitutes a closed-loop system for controlling

3. the mass flow of the fluid. The set value of the mass flow controller can
be provided by an analog voltage, analog current, or computer or PLC.
The difference in the selection guide of the electromagnetic flowmeter
and mass flowmeter
Selection principle of electromagnetic flowmeter
1. Accuracy class and function
Choose the accuracy of the electromagnetic flowmeter according to
measurement requirements and use occasions. For example, for trade
settlement, product handover, and energy metering, high precision should
be selected (for example, 1.0 grade, 0.5 grade or higher)
2. Test medium flow rate, meter range, and diameter
When measuring general media, the full-scale flow of the electromagnetic
flowmeter can be measured in a wide range of medium flow velocity
0.5-12m/s. The gauge size (caliber) selected may not be the same as that
of the processing pipeline and should be determined according to whether

4. the measuring flow range is within the flow rate range. That is, when the
pipeline flow rate is low and cannot meet the requirements of the flow
meter, it is necessary to reduce the meter caliber, thereby increasing the
flow rate in the tube and obtaining satisfactory measurement results.
Measure the liquid with good conductivity, the maximum flow velocity
does not exceed 5m/s, the economic flow velocity range is 1.5m/s～3m/s
3. Electrode material and ground ring material
The corrosion resistance of the electrode to the measuring medium
determines which electrode material to choose, and at the same time, the
electrical level must not have surface effects. In other words, the
corrosion resistance of the electrode is an important basis for selecting
materials.
The material of the grounding ring should be the same as that of the
electrode, otherwise, it is easy to produce electrochemical polarization
potential. Generally, 316L or Hastelloy is used, but tantalum, platinum,
and other precious metals are rarely used from economic considerations.
The metal process pipeline is in direct contact with the medium, and the
grounding wire is directly connected to the metal pipeline or flange, so
there is no need for a grounding ring
Selection principle of mass flow meter

5. 1. Select the structure of the flowmeter according to the type of fluid
being measured
There are many methods for the measuring tube of Coriolis mass
flowmeter, which need to be considered based on the type of medium to
be measured. In principle, pure liquids with low viscosity do not have
many requirements for the shape of the measuring tube; when measuring
liquids with a few bubbles, slurries containing solid particles, and
high-viscosity liquids, the measuring tube should be selected that is not
easy to accumulate bubbles or solid particles, and the inner wall The
shape that is not easy to adhere to the medium; if used in the food
industry, the measuring tube should be easy to clean
2. Security guidelines

6. When measuring corrosive fluids, attention should be paid to the
corrosion resistance of the measuring tube, and the sensor housing should
also have certain corrosion resistance. If the detection tube breaks, there
should be safety protection measures before handling. Different media
have different corrosivity, and different materials have different
anti-corrosion targets, so pay attention to different treatments. When
measuring abrasive media, the wear resistance of the measuring tube
should be considered
3. Flow rate scale
Considering the flow scale, two criteria should be followed: one is
because the Coriolis mass flowmeter has a greater impact on the accuracy
of the lower limit flow measurement due to its zero point stability,
Second, the commonly used process flow should fall within the economic
flow scale of the flowmeter
4. Accuracy
The accuracy level requirements should be confirmed based on the
measurement objectives and intentions. At the same time, attention
should be paid to the calculation method of the product accuracy level
and the operating conditions or constraints to reach the level. Generally
speaking, the Coriolis mass flowmeter uses the percentage of the flow
reading with zero-point stability to indicate the accuracy level. Some

7. products use different flow sections corresponding to different error
limits to show that some products are at low flow rates. Use the
percentage of full scale to indicate the error level
5. Pressure loss
In infield measurement, there are always certain requirements for the
pressure loss of the flowmeter. When the density, viscosity, and flow rate
of the medium are confirmed, the pressure loss of the flowmeter depends
on its structure. For Coriolis mass flowmeters, it depends on the caliber,
flow area, and measuring tube shape; when the sensor structure is
confirmed, The greater the flow, the greater the pressure loss. When
calculating the pressure loss in the selection, the following points should
be fully considered: the flow rate in the processing pipeline and the
allowed pressure loss; whether the sensor meets the requirements of
measurement accuracy under the allowed pressure loss condition; the
change in the viscosity and density of the process fluid The influence of
pressure loss; in the application, the liquid should be prevented from
vaporizing due to excessive pressure loss. When other conditions are
combined, a flowmeter with less pressure loss should be selected.
6. Consideration of other functional elements
The first is to consider the additional measurement functions of the
flowmeter, such as the accuracy of the Coriolis mass flowmeter to

8. measure the temperature and density of the medium; the second is to
consider the factors that affect the device such as the volume and weight
of the mass flowmeter and the constraints of the dedicated cable.
The advantages of the electromagnetic flowmeter and mass
flowmeter
The main advantages of electromagnetic flowmeter
1. The output of 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 or turbulent) under a symmetrical
distribution. Therefore, the electromagnetic flowmeter has a very
wide range, with a range ratio of up to 20:1, and some even up to
100:1.

9. 2. The diameter range of industrial electromagnetic flowmeters is
extremely wide, from several millimeters to several meters, and
there is real-flow calibration equipment with a diameter of 3m in
China, which has laid the foundation for the application and
development of electromagnetic flowmeters.
3. The sensor structure of the electromagnetic flowmeter is simple,
and there are no moving parts in the measuring tube, nor any
throttling parts that hinder fluid flow. Therefore, when the fluid
passes through the flow meter, it will not cause any additional
pressure loss. It is one of the flow meters with the lowest energy
consumption in the flow meter.
4. The electromagnetic flowmeter has no mechanical inertia and is
sensitive. It can measure the instantaneous pulsating flow rate and
the flow rate in both positive and negative directions.
5. It can measure the flow of dirty media, corrosive media, and
suspended liquid-solid two-phase flow. This is because there are no
parts obstructing the flow inside the measuring tube of the
instrument, and only the inner liner and electrode of the measuring
tube are in contact with the measured fluid. The material can be
selected according to the nature of the measured fluid. For example,
using polytetrafluoroethylene or polytetrafluoroethylene as the inner
lining can measure various acids, alkalis, salts, and other corrosive

10. media; using wear-resistant rubber as the inner lining is particularly
suitable for measuring wear and tear with solid particles Larger
liquid-solid two-phase flow such as mineral pulp and cement slurry,
and various suspended liquids such as fibrous liquid and pulp.
6. The electromagnetic flowmeter is a volume flow measuring
instrument. During the measurement, it is not affected by the
temperature, viscosity, density, and conductivity (in a certain range)
of the measured medium. Therefore, the electromagnetic flowmeter
can be used to measure the flow of other conductive liquids only
after being calibrated by water.
Advantages of mass flowmeters
1. The mass flow meter directly measures the mass flow of the fluid,
and the current signal converted by the transmitter does not need to
be squared;

11. 2. Long service life and low maintenance rate: The measuring body of
the mass flowmeter is a U-shaped tube, and the two open ends of
the U-shaped tube are fixed. Fluid flows in and out from this. There
are no obstacles in the pipeline, no moving parts, and failure factors.
Less, easy to install and maintain;
3. Multi-function: The mass flowmeter can simultaneously measure
multiple field variables such as flow, density, temperature, etc. The
transmitter has two output signals that can be configured separately,
which can be used to display the measured values of flow, density,
temperature, etc. One mass flow meter can replace multiple
measuring instruments;
4. High precision: It can reach ±0.1 (zero points stability/actual
flow)×100% for liquids, and ±0.5 (zero points stability/actual
flow)×100% for gases, which are used in cracking furnace feed
control The zero-point stability of the mass flowmeter is 2.18KG/H
for CMF200M418NU, 2.18KG/H for CMF200M419NU and
6.80KG/H for CMF300M426NU;
5. The damping time of the mass flow meter is adjustable;
6. The mass flow meter has a strong loop self-diagnosis function,
which is convenient for fault finding.

12. Mr. Michael Sun
Sales Manager
Dalian Zero Instrument Technology Co., Ltd China
p: +86-411-88586750 m: +86 17640305359
f: +86-411-88586751
a: Room 4605 No.9-1 Haifu Road Dalian Bonded Area Pilot
Free Trade Zone Liaoning China 116001
w:www.zeroinstrument.com e: info@zeroinstrument.com