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Electromagnetic flowmeter is a flow measurement instrument based on Faraday's electromagnetic induction principle, and is often used to measure the flow of conductive liquids or slurries. Its working principle is mainly based on the law of electromagnetic induction, and the specific process is as follows:
1. **Principle of electromagnetic induction**:
According to Faraday's law of electromagnetic induction, when a
conductive fluid flows through a uniform magnetic field, the
charged particles in the fluid will generate an electromotive force
(i.e., induced voltage) under the action of the magnetic field.
This electromotive force is related to factors such as the flow
rate of the fluid, the strength of the magnetic field, and the
inner diameter of the pipe.
2. **Structural composition**:
- **Magnet**: used to generate a constant magnetic field.
- **Electrodes**: located on both sides of the pipe of the
flowmeter, used to measure the induced voltage generated in the
fluid.
- **Pipeline**: The pipe through which the fluid passes, usually
made of insulating material to ensure that it does not affect the
electric field.
- **Signal processor**: used to convert the induced voltage into a
flow signal.
3. **Working process**:
- The electromagnetic flowmeter conducts current through the fluid
in the pipe, and the magnet generates a magnetic field
perpendicular to the flow direction outside the pipe where the
fluid flows.
- When the fluid flows through the magnetic field, according to
Faraday's law, the charged particles (such as ions) in the fluid
are deflected under the action of the magnetic field, generating an
electromotive force. The magnitude of this electromotive force is
proportional to the flow rate of the fluid.
- The electromotive force of the fluid is received by the electrode
and transmitted to the signal processor through the wire.
- The signal processor calculates the flow rate of the fluid based
on the measured voltage signal and converts it into a digital
signal suitable for display or recording.
4. **Flow calculation formula**:
The magnitude of the electromotive force (( E )) is proportional to
the fluid flow rate (( v )), and the formula is:
[
E = k cdot B cdot v cdot D
]
Where:
- ( E ) is the induced voltage.
- ( k ) is a constant.
- ( B ) is the magnetic field strength.
- ( v ) is the flow rate.
- ( D ) is the inner diameter of the pipe.
According to this formula, the flow rate (( Q )) can be calculated by the induced voltage.
5. **Advantages**:
- **No mechanical moving parts**: Therefore, maintenance is small
and the service life is long.
- **Wide application range**: It can be used for various conductive
liquids and slurries, and is widely used in chemical, sewage
treatment, food processing and other industries.
- **High precision**: It can provide high-precision flow
measurement.
- **Not affected by the density, viscosity, etc. of the fluid**: It
is only related to the flow rate and the conductivity of the fluid.
6. **Applicable conditions**:
- The fluid must be conductive or have a certain conductivity (such
as water, acid, alkali, mud, etc.).
- The installation position of the flowmeter should ensure the
stability of the fluid flow and avoid strong turbulence and
vibration.
In general, the working principle of the electromagnetic flowmeter is to calculate the flow rate based on the flow rate of the fluid, the magnetic field strength of the pipeline and the electromotive force through Faraday's law of electromagnetic induction, which has the advantages of high precision and long-term stability.
When selecting an electromagnetic flowmeter, it is usually necessary to determine the appropriate model based on the following key parameters. These parameters affect the performance, installation and operating costs of the flowmeter. The following are the general parameters to consider when selecting an electromagnetic flowmeter:
1. **Pipeline ID (Pipeline Size)**
- **Inner Diameter Range**: The measurement range of the
electromagnetic flowmeter is usually related to the inner diameter
of the pipe. Common pipe sizes range from a few millimeters to
several meters.
- **The inner diameter of the flowmeter** needs to match the inner
diameter of the measured pipe to ensure that the fluid can flow
stably through the sensor. Generally, an electromagnetic flowmeter
with the same or slightly larger inner diameter as the pipe is
selected to obtain stable flow measurement.
2. **Flow Range**
- **Maximum Flow**: Consider the maximum flow requirement in the
application. When selecting a flowmeter, the measurement range of
the flowmeter should cover the entire flow variation range to
ensure accuracy.
- **Minimum Flow**: The measurement accuracy of the electromagnetic
flowmeter is poor under low flow conditions, so make sure the
selected flowmeter can meet the minimum flow requirement.
3. **Flow rate range**
- **Flow rate range**: Flow rate is one of the key factors for the
measurement accuracy of electromagnetic flowmeter. Different
flowmeters have different applicable flow rate ranges. Generally
speaking, the flow rate range of electromagnetic flowmeters is
roughly between 0.3 m/s and 10 m/s. Select the appropriate flow
rate range according to the characteristics of the fluid and the
actual flow conditions.
4. **Fluid properties**
- **Conductivity**: Electromagnetic flowmeters can only measure
conductive fluids, so it is necessary to ensure that the fluid has
a certain conductivity (such as water, mud, acid, alkali, etc.).
The conductivity of the fluid usually needs to be greater than 5
μS/cm.
- **Fluid temperature**: Different types of electromagnetic
flowmeters have different applicable operating temperature ranges.
The common operating temperature is -20℃ to +150℃, and some special
models can withstand higher or lower temperatures. Choose a
suitable flowmeter according to the temperature of the fluid.
- **Fluid pressure**: Select the flowmeter according to the
pressure in the actual working conditions to ensure that the
flowmeter will not be damaged during operation. Common pressure
ranges are usually 6 bar, 16 bar or 40 bar.
5. **Installation location and method**
- **Installation method**: Electromagnetic flowmeters are usually
installed horizontally or vertically. For non-viscous fluids,
horizontal installation can be selected; for fluids with solid
particles, vertical installation is recommended. The appropriate
installation method needs to be selected according to the layout of
the pipeline and the properties of the fluid.
- **Straight pipe section length**: Electromagnetic flowmeters have
high requirements for fluid flow stability, and usually require a
straight pipe section of 5 to 10 times the inner diameter of the
pipeline before and after the flowmeter to reduce the flow velocity
disturbance caused by elbows, valves, etc.
6. **Electrode material and lining material**
- **Electrode material**: The electrode material needs to be
selected according to the corrosiveness of the fluid. Common
materials include stainless steel, titanium, platinum, etc. For
highly corrosive fluids, materials with stronger corrosion
resistance (such as titanium alloy or platinum) are usually
selected.
- **Lining material**: The lining material has an important
influence on the chemical stability of the fluid and the service
life of the flowmeter. Common lining materials include rubber,
polytetrafluoroethylene (PTFE), ceramics, etc. For fluids with
different corrosiveness and temperature, choosing the appropriate
lining material can improve measurement accuracy and extend the
service life of the flowmeter.
7. **Output signal**
- **Analog signal output**: 4-20mA output is the most common
standard signal output method, suitable for most industrial
automation systems.
- **Pulse signal output**: Suitable for applications that require
counting pulses, often used for flow accumulation, remote
transmission or linkage control.
- **Digital signal output**: Such as Modbus RTU, Profibus, Hart and
other protocol outputs, suitable for data communication and
integration with other intelligent devices (such as PLC, DCS).
8. **Protection level and environmental conditions**
- **Protection level**: The flowmeter should select a suitable
protection level according to the use environment. Common
protection levels are IP65, IP67, and IP68. Select a suitable
protection level according to the humidity, dust, and whether it is
exposed to the outdoors in the application environment.
- **Explosion-proof type**: In explosive environments (such as the
petrochemical industry), you may need to choose an explosion-proof
electromagnetic flowmeter.
9. **Power supply method**
- **Power supply requirements**: Depending on the on-site power
conditions, the electromagnetic flowmeter can be powered by
alternating current (AC) or direct current (DC). Common power
requirements are 24V DC or 110/220V AC.
- **Low power version**: For remote installations or places without
stable power supply, you can choose a low power version or a
solar-powered model.
Measuring Principles
The measuring principle of electromagnetic flowmeter is based on the electromagnetic induction law of Farady. The sensor is mainly composed of measuring tube with isolate lining, a pair of electrodes installed by penetration of the measuring tube wall, a pair of coils and iron core to produce working magnetic field. When the conductive fluid flows through the measuring tube of the sensor, the voltage signal in direct proportion to the average flow velocity of the fluid will be inducted on the electrodes. The signal is amplified and treated by the transmitter to realize various display functions.
Converter Circuit Schematic
The converters supplies a stable exciting current to the coil in the sensor of electronetic flowmeters to get B constant and amplifies the electromotive force and convert it into standard signals of current or frequency so that the signals can be used for displaying, controlling and processing. The schematic of converter circuit is shown in Fig. 2.1.
Table of Parameter Setting Menu
The converter setting menu consists of 45 items. Many of them are set up by manufacturer before shipping. It is not necessary to change them when applying. There are only a few of them to be set by user according to the application. The menu items are listed in the table below:
Item No. | Menu Display | Setting Method | Password Level | Value Range |
1 | Language | Option | 1 | Chinese/English |
2 | Sensor Size | Option | 1 | 3 - 3000mm |
3 | Flow Range | Modify | 1 | 0 - 99999 |
4 | Auto Rng Chg | Option | 1 | ON / OFF |
5 | Damping | Option | 1 | 0 - 100 s |
6 | Flow Dir. | Option | 1 | Fwd/ Res |
7 | Flow Zero | Modify | 1 | +/-0.000 |
8 | L.F. Cutoff | Modify | 1 | 0 - 99% |
9 | Cutoff Enble | Option | 1 | ON / OFF |
10 | Rate-Of-Chng | Modify | 1 | 0 - 30% |
11 | Limit Time | Modify | 1 | 0 - 20 s |
12 | Total Unit | Option | 1 | 0.0001L - 1 m3 |
13 | Flow Density | Modify | 1 | 0.0000 - 3.9999 |
14 | Current Type | Option | 1 | 4-20mA/0-10mA |
15 | Pulse Output | Option | 1 | Frq/ Pulse |
16 | Pulse Factor | Option | 1 | 0.001L - 1 m3 |
17 | Freq Max | Modify | 1 | 1 - 5999 Hz |
18 | Comm Address | Modify | 1 | 0 - 99 |
19 | Baudrate | Option | 1 | 600 - 14400 |
20 | EmpPipe Det. | Option | 1 | ON / OFF |
21 | EmpPipe Alm | Modify | 1 | 200.0 KΩ |
22 | Hi ALM Enble | Option | 1 | ON / OFF |
23 | Hi Alm Limit | Modify | 1 | 000.0 - 199.9% |
24 | Lo Alm Enble | Option | 1 | ON / OFF |
25 | Lo Alm Limit | Modify | 1 | 000.0 - 199.9% |
26 | RevMeas.Enbl | Option | 1 | ON/OFF |
27 | Sensor S/N | Modify | 2 | 000000000000-999999999999 |
28 | Sensor Fact. | Modify | 2 | 0.0000 - 3.9999 |
29 | Field Mode | Option | 2 | Mode 1,2,3 |
30 | Multiplying | Modify | 2 | 0.0000 - 3.9999 |
31 | F. Total Set | Modify | 3 | 0000000000 - 9999999999 |
32 | R.Total Set | Modify | 3 | 0000000000 - 9999999999 |
33 | Input Contrl | Option | 3 | Disable/Stop Tot/Reset Tot |
34 | Clr Totalizr | Password | 3 | 00000 - 59999 |
35 | Clr Tot. Key | Modify | 3 | 00000 - 59999 |
36 | Date –y/m/d * | Modify | 3 | 99/12/31 |
37 | Time-h/m/s * | Modify | 3 | 23/59/59 |
38 | Password L1 | Modify | 3 | 0000 - 9999 |
39 | Password L2 | Modify | 3 | 0000 - 9999 |
40 | Password L3 | Modify | 3 | 0000 - 9999 |
41 | Current Zero | Modify | 4 | 0.0000 - 1.9999 |
42 | Current Max | Modify | 4 | 0.0000 - 3.9999 |
43 | Meter Factor | Modify | 4 | 0.0000 - 3.9999 |
44 | Convtr S/N | Modify | 4 | 0000000000-9999999999 |
45 | Sys Reset | Password | 4 |
Scenario application:
FAQ
1. Q: What information need to be provided to choose the suitable
model?
A: Application field, Nominal pressure ,Medium & medium
temperture , Power supply , Output,
Flow range, Accuracy, Connection and other parameters.
2. Q: Are you a trade company or a manufacturer?
A: We are an ISO approved manufacturer specialized in level and
flow measuring instruments.
OEM & ODM service are available. Welcome to visit us in China.
3. Q: What is your MOQ?
A: To start our cooperation, sample order is acceptable.
4. Q: What is your delivery date for the Intelligent Mini Micro
Turbine Fuel Oil Diesel Flow Meter?
A: The delivery date is about 3-15 working days after receipt of
payment.
5. Q: What is your payment terms?
A: We support T/T, PayPal ,Western Union.
For mass production order, it is 30% deposit in advance and 70%
balance before shipment.
6. Q: Do you have a warranty for the Flow Meter?
A: Yes, we have the warranty of 12 months.