Principle, structure

The measurement principle of FE20 electromagnetic flowmeter is based on Faraday's law of electromagnetic induction: when a conductive liquid cuts magnetic field lines in a magnetic field, an induced potential is generated in the conductor,

The induced potential is E:

E=KBVD

In the formula: K - instrument constant

In the formula: B - Magnetic induction intensity

In the formula: V - the average flow velocity within the cross-section of the measuring tube

In the formula: D - measure the inner diameter of the pipeline cross-section

When measuring flow rate, a conductive liquid flows through a magnetic field perpendicular to the flow direction at a velocity of V. The flow of the conductive liquid induces a voltage proportional to the average flow velocity, and the induced voltage signal is detected by two or more induction electrodes in direct contact with the liquid and sent to a converter through a cable for intelligent processing, achieving the display of instantaneous fluid flow rate, accumulated flow rate, and communication between flow data and control system. There are no active or obstructed components inside the measuring tube, so there is almost no pressure loss and high reliability.

structure

FE20 electromagnetic flow characteristics... advantages

Electromagnetic flowmeter is an instrument for measuring volumetric flow rate, and the measurement results are independent of physical parameters such as flow velocity distribution, flow pressure, temperature, density, viscosity, etc

There are no moving parts inside the measuring tube, making it easy to maintain and manage, so the sensor has a long service life; No obstruction components, as there is no pressure loss

The minimum conductivity of the tested liquid can reach 5 μ S/cm, and with various lining materials, it can be used to measure the flow rate of various acid, alkali, salt solutions, as well as mud, slurry, pulp and other media, with high accuracy,

Usually ± 0.5% ± 0.2%

Due to the fact that the induced voltage signal is formed in the entire space filled with magnetic field, which is the average value on the cross-section of the pipeline, the straight pipe section required for the sensor is relatively short, usually the first 5D and then 3D

The sensor part only has the inner lining and electrodes in contact with the measured liquid. As long as the electrode and inner lining materials are selected reasonably, they can be corrosion-resistant and wear-resistant, ensuring long-term use

Bidirectional measurement system, capable of measuring forward flow and reverse flow

High definition backlit LCD display, Chinese English menu operation, easy to use, simple to operate, easy to learn and understand

The converter has reliable performance, high accuracy, low power consumption, stable zero point, convenient parameter setting, LCD display, and can display parameters such as cumulative flow rate, flow rate, and flow percentage

Adopting a 16 bit embedded microprocessor, it has fast computing speed, high accuracy, programmable low-frequency rectangular wave excitation, improved measurement stability, and low power consumption

● All digital processing, strong anti-interference ability, reliable measurement, high accuracy, flow measurement range can reach 150:1

Ultra low EMI switching power supply, with a wide range of voltage variations and good EMC resistance

● Equipped with digital communication signal outputs such as RS485, RS232, HART, and Modbus

FE20 Electromagnetic Flow Characteristics... Limitations

Electromagnetic flow meters cannot measure gases, vapors, and liquids containing large amounts of gas

At present, electromagnetic flow meters cannot be used to measure liquid media with very low conductivity. The conductivity of the measured liquid medium cannot be lower than 5 μ S/cm, which is equivalent to the conductivity of distilled water and is powerless for petroleum products or organic solvents

The insulation lining of the measuring tube is limited by temperature, and the electromagnetic flowmeter cannot measure high-temperature liquids. It is suitable for measuring medium temperatures ≤ 180 ° C. The measurement principle of the electromagnetic flowmeter is based on Faraday's law of electromagnetic induction, so it is easily affected by external electromagnetic interference sources

application

The liquid medium used to measure conductivity requires a conductivity greater than 5 μ s/cm (the conductivity of tap water and raw water is about 100... 5000 μ s/cm, which can be used to measure various acids, alkalis,...)

The flow rate of salt solution, slurry, pulp and other media, but the media should not contain a lot of iron filings, ferromagnetic substances and a large number of bubbles, mainly used in petrochemicals, steel

Industries such as electricity, metallurgy, textiles, food, pharmaceuticals, papermaking, as well as municipal environmental protection and water conservancy.

Technical Parameter

Using media

The lowest liquid conductivity can reach 10 μ S/cm

installation drawing

Note: For liquids or slurries containing solid particles, it is recommended to install them vertically with a flow direction from bottom to top. This is because impurities are prone to precipitate at the bottom of the measuring tube. Please refer to the installation instructions for straight pipe sections for specific installation.

Detailed explanation of main technical parameters

Applicable medium: Conductive liquids with a conductivity of 10 μ s/cm during normal measurement. Generally, the conductivity of distilled water is 5 μ s/cm, and the conductivity of tap water is 100 μ s/cm. The conductivity of other acids, bases, and salts can refer to the following table:

● Flow rate requirement: 0.3-12m/s

Under normal circumstances, it is ideal to use an electromagnetic flowmeter with a measurement range of 1... 4m/s for the flow velocity V;

(1) For viscous fluids, the flow velocity can be chosen to be greater than 2m/s. A higher flow velocity helps to automatically eliminate the effect of viscous substances attached to the electrode, which is beneficial for improving measurement accuracy.

(2) For liquids with low viscosity (such as water), the pipeline flow rate is generally selected to be between 1.5-3m/s.

(3) For liquids with slightly high viscosity or sediment, the sensor aperture should be selected so that the flow rate is not less than 3-4m/s or higher, in order to facilitate self-cleaning and prevent sedimentation with the liquid.

(4) For highly abrasive liquids such as slurry, the commonly used flow rate should not exceed 3m/s to reduce wear on the lining and electrodes.

(5) For low conductivity liquids, when selecting the diameter of the transducer, try to use a lower flow rate not exceeding 1m/s as much as possible. As the flow rate increases, the flow noise will increase, resulting in output shaking.

The following figure shows the relationship curve between the flow rate, flow rate, and diameter of the flowmeter:

Under the condition that the range Q has been determined, the size of the flowmeter diameter D can be determined based on the range of the flow velocity V mentioned above

The formula for calculating flow velocity is as follows:

（1）V = 1273.24*Q/DN²

Unit: V: [m/s], Q: [I/S], DN: [mm]

(2)V = 353.68 *Q/DN²

Unit: V: [m/s], Q: [m ³/h], DN: [mm]

Note: Q: Flow DN: Inner diameter of pipeline V: Flow velocity

Accuracy ≤ ± 0.2%, ≤ ± 0.5% under reference conditions

Accuracy Curve of Electromagnetic Flow Meter System (± 0.20%)

Accuracy Curve of Electromagnetic Flow Meter System (± 0.5%)

basic function

Selection of electromagnetic flowmeter

1. The correct selection of electromagnetic flowmeter requires a detailed understanding of the following process parameters: 1. The correct selection of electromagnetic flowmeter requires a detailed understanding of the following process parameters:

The actual maximum working pressure must be less than the rated working pressure of the electromagnetic flowmeter;

The minimum and maximum operating temperatures must comply with the temperature requirements specified in the flow measurement regulations (see the lining material table for details);

From an economic perspective, an electromagnetic flowmeter with an appropriate diameter corresponding to the flow rate can be selected to relatively reduce investment (see flow range table);

Reasonably select the corresponding accuracy level based on the measurement purpose and function;

Select electrode materials for electromagnetic flow meters based on the corrosiveness of the medium;

Select the lining material for the flow rate based on the corrosiveness, wear resistance, and temperature of the medium;

Choose between using an integrated electromagnetic flowmeter or a split type electromagnetic flowmeter based on the requirements and environment of the installation site.

2. Selection of Electromagnetic Flow Meter Diameter

3. Electromagnetic flowmeter converter

4. Selection of lining

5. Selection of electrode materials

6. Selection of flowmeter type

Split type

Split type is a common application form of electromagnetic flow calculation. The sensor is separately connected to the process pipeline, and the converter is installed in other places several meters or more apart, connected by cables in the middle. A split type flowmeter can keep the converter away from harsh environments and facilitate observation and adjustment of set parameters.

All-In-One

Integrated type refers to the assembly of a converter and a sensor into a whole, with the connecting wires inside the instrument, making it relatively easy to use. Due to the infrequent use of cables, external interference is also relatively small. Integrated flow meters are generally used for small-diameter instruments. If the sensor is installed at a high place or in difficult to observe environments, such as high temperatures or large vibrations, and the electronic components of the converter are difficult to withstand, integrated electromagnetic flow meters should not be used.

7. Selection of grounding ring

(1) The forms of grounding rings are divided into universal and protective types. Generally, universal type is used. If the tested medium is abrasive, a protective grounding ring with a neck should be used to protect the lining at the inlet and outlet ends and extend the service life. If the diameter of the electromagnetic flowmeter is below 200, when using a polytetrafluoroethylene lining, a grounding ring should be selected to ensure that the lining is not damaged during installation and connection with the pipeline.

(2) The material of the grounding ring should be compatible with the corrosiveness of the tested medium, but with lower requirements than the electrode material, as it can be replaced after corrosion. The grounding ring is usually made of stainless steel or Hc alloy.

8. Selection of protection level for electromagnetic flowmeter

9. Selection of Special Pressure Resistance for Electromagnetic Flowmeters

The pressure resistance of sensors is related to their inner diameter. According to relevant national standards, the maximum pressure resistance of standard steel pipes and flanges is as follows:

Note: If the pressure of the fluid inside the sensor exceeds the maximum pressure resistance mentioned above, it belongs to the pressurized type and requires special customization

2. Except for sensors lined with polytetrafluoroethylene, sensors lined with other materials can operate under negative pressure in pipelines

10. Selection of sanitary electromagnetic flowmeter

The food, pharmaceutical and other industries require that the materials used for electromagnetic flow meters to come into contact with liquids are non-toxic and harmless. For example, the lining should be made of polytetrafluoroethylene, and the sensor housing and connecting flange should be made of stainless steel. Structurally, it is required to be easy to disassemble, clean, and sterilize. The parts connected to the pipeline should be able to be quickly loaded and unloaded, such as using flexible joints instead of flange connections.

Dimensional drawings (flange type, sanitary clamp connection type, threaded connection type, clamping type, battery powered)

Flange type size

One body type, split body type

FE20 external dimensions (flange type: DN10 to DN50: PN40; DN65 to DN200; PN16 ; DN250 to DN1000 :PN10 , Other PN6)

Dimensional drawing of sanitary clamp connection type

Explanation: The standard configuration of the sanitary electromagnetic flowmeter is two measuring electrodes, and there is no need to configure a grounding ring and grounding electrode when selecting.

Dimensional drawing of threaded connection type

Battery Powered Dimensional Drawing

Clamp on dimension diagram

Explanation: The clamp type electromagnetic flowmeter comes standard with two measuring electrodes, and a grounding ring must be included when selecting. Otherwise, the flow meter will not function properly.

FE20 Installation Requirements

Requirements for upstream and downstream straight pipe sections of sensors:

In order to ensure the accuracy stated in the manual under different application conditions, a straight pipe section with a diameter five times the diameter should be installed upstream of the electrode surface and a straight pipe section with a diameter three times the diameter should be installed downstream when installing the sensor, as shown in the following figure. This installation can fully eliminate interference caused by bends, valves, or necking. When the straight pipe sections before and after the flowmeter cannot meet the requirements, there will be a certain deviation in performance indicators.

Grounding requirements for sensors:

There must be a reliable grounding path between the electromagnetic flowmeter sensor and the measured medium. There are three grounding methods to choose from: grounding electrode, grounding ring, and pipeline grounding. Please refer to the selection table for details.

Outline dimension diagram of split type converter

L1 type split remote display setting type (circular)

L2 type split remote display setting type (square)

Maximum distance of split type, curve of dielectric conductivity and cable copper core cross-section

Note:

(1) The length of the cable when using a split type connection depends on the conductivity of the medium and the size of the copper core cross-section of the cable. For example, the conductivity of tap water is around 100 μ S/cm, and the maximum distance of the split type is about 100m.

(2) In practical applications, the shorter the distance of the split cable, the better. The longer the cable, the more susceptible it is to signal interference.

Model Selection Table