Electromagnetic flow meter

One, the introduction:
LDE series electromagnetic flow meter adopts new technology of the world.Using the constant current low-frequency rectangular wave three values or double frequency rectangular wave excitation, the advantages of both the rectangular wave magnetic field, and overcomes the drawback of sinusoidal magnetic field;Can also eliminate the power supply voltage fluctuation, power frequency and the excitation coil impedance changes caused by the error;And has excellent stability of zero point and is not affected by fluid noise interference.Which has the characteristics of high stability, high reliability.
Second, the measuring principle:
LDE series electromagnetic flowmeter based on Faraday electromagnetic induction principle, with the measuring pipe axis and the magnetic field lines in the vertical tube wall installed on a pair of detecting electrodes, when conducting liquid along the measuring tube axis movement, conductive liquid cutting lines of magnetic force induced electric potential, the induction electric potential by two detection electrodes detection, numerical size and flow into a direct ratio, its value is: E = KBVD type:
E - induction electric potential;
K - factor related to the magnetic field distribution and the axial length;
B - magnetic induction intensity;
V - conductive liquid average flow velocity;
D - electrode gap;(the measuring tube diameter)
Sensor will be induced potential E as traffic signal, sent to the converter, amplifying, transform filter with a series of digital processing, USES dot matrix LCD display with backlight instantaneous flow and cumulative flow.Converter has 4 ~ 20 ma output, alarm output and frequency output, and is equipped with RS - 485 communication interface, and supports HART and MODBUS protocol.
Three, are widely used:
LDE series electromagnetic flowmeter is mainly used to measure volume flow of conducting liquid and slurry in the closed pipeline.Such as water, sewage, slurry, pulp, all kinds of acid, alkali, salt solution, food slurry, etc., widely used in petroleum, chemical, metallurgical, textile, food, pharmaceutical, paper making industries and environmental protection, municipal administration, water conservancy construction and other fields.
Four, the main features:
1, instrument structure is simple, reliable, have no moving parts, working life is long;
2, no closure choke parts, there is no loss of pressure and fluid blocking phenomenon;
3, no mechanical inertia, fast response and good stability, can be applied to automatic testing, adjusting and SPC system;
4, the measurement precision is not affected by the type of measured medium and its temperature, viscosity, density, the influence of physical parameters such as pressure;
5, adopt ptfe or rubber lining material and Hc, Hb, 316 l, the different combination of electrode materials such as Ti can meet the needs of the different media;
6, with pipeline, plug-in, such as a variety of flow meter type;
Block 7, using EEPROM memory, measuring operation safe and reliable data storage protection;
8, integration and separation of two types;
9, high-definition LCD backlit display.
Five, the main technical parameters:
Instrument accuracy: pipeline magnitude 0.5, 1.0;Plug in 2.5 on the Richter scale;
Measuring medium: conductivity is greater than 5 mu S/cm of various liquid and liquid-solid two-phase fluid;
Velocity range: 0.2 ~ 8 m/s;
Working pressure: 1.6 MPa;
Ambient temperature: - 40 ℃ ~ + 50 ℃;
Medium temperature: ptfe lining 180 ℃ or less.
Rubber lining 65 ℃ or less;
Explosion-proof marks: Exmibd Ⅱ BT4;
Explosion-proof number: GYB01349;
Outside magnetic interference: 400 a/m or less;
Enclosure protection: integration type: IP65;
In mold: sensor IP68 (5 meters underwater, rubber lining only) converter IP65;
Output signals: 4 ~ 20 ma DC, 0 ~ 750 Ω load resistance;
Communication output: RS485 or CAN bus;
Electrical connections: M20 x 1.5 internal thread, phi 10 cable hole;
Power supply voltage: 90 ~ 220 v AC, 24 V.D C + / - 10%;
The maximum power consumption: 10 or less va.
Six, according to excitation methods of classification:
To produce a uniform constant magnetic field, it needs to choose a suitable way of excitation.Such as divided according to the field current mode, have a dc field, ac (or other frequency) power frequency excitation, low-frequency rectangular wave excitation and dual-band rectangular wave excitation.
1, the dc excitation
Dc excitation method with direct current (dc) or by a permanent magnet to produce a constant homogeneous magnetic field.The biggest advantage of dc excitation transmitter is affected by the ac electromagnetic interference is very small, so you can ignore the influence of the liquid in the self inductance.But using dc magnetic field is easy to make by measuring the electrolyte fluid of the pipe is polarized, the electrolyte by electrolysis in the electric field, produce positive and negative ions, in under the action of electric field force, ran to the anode, anion cation ran to the cathode, which will result in positive and negative electrodes were surrounded by ions of opposite polarity, seriously affect the normal work of the instrument.So, dc excitation only commonly used for measuring the liquid electrolyte, such as the liquid metal flow of mercury (room temperature and high temperature of liquid steel, lithium, potassium), etc.
2, ac excitation
Industrial use of electromagnetic flowmeter, most used (50 hz) power supply power frequency ac excitation method to produce alternating magnetic field, to avoid the dc excitation on the surface of the electrode polarization interference.But the use of ac excitation will bring a series of electromagnetic interference problem, such as orthogonal interference, in-phase interference, zero drift, etc.).Ac excitation is now replaced by low frequency square wave excitation.
3, low frequency square wave excitation
Low frequency square wave excitation waveform has two values (positive - negative) and three values (positive - zero - negative - zero) two kinds, the frequency of power frequency usually 1/2 ~ 1/32.Low frequency square wave excitation can avoid orthogonal electromagnetic interference of ac magnetic field, power frequency interference caused by distributed capacitance, inhibition of ac magnetic field within the tube wall and fluid caused by eddy current, dc excitation polarization phenomenon.
Seven, installation location choice:
In order to make the transmitter work stability, when choosing the location should be paid attention to the following requirements:
1, try to avoid strong ferromagnetic objects and concrete equipment of electromagnetic field (such as a big motor, transformer, etc.), so as to avoid the magnetic field of magnetic field effect sensor and traffic information.
2, should be installed in a dry and ventilated place, should not be in damp, easy seeper place of installation.
3, should try to avoid weathered, avoid environmental temperature is higher than 45 ℃ and relative humidity is more than 95.9%.
4, choose to facilitate maintenance and convenient place.
5, flow meter should be installed in the pump back end, never on the suction side of the installation;The valve should be installed in the downstream flow meters.
Eight, the structure form:
1, the sensor:
Sensor is mainly composed of measuring tube and electrode, excitation coils, iron core, magnetic yoke and shell.
A, measuring catheter: by stainless steel tube, the lining and the connecting flange, as the carrier of measured liquid measurement working conditions on site.
B, measuring electrode: installed in the measuring tube inside wall, and the axial direction perpendicular to a pair of electrodes to measure liquid signal generation.
: c, excitation coil in a magnetic field measurement of intraductal two excitation coil.
D, iron core and magnetic yoke: the excitation coil of the magnetic field generated import liquid, and the magnetic circuit.
E, shell: instrument packaging.
2, the converter:
Is the smart secondary table, it will flow signal amplification processing stymied microcontroller after operation, can display flow, total amount, and can output pulse and analog current signal, used in the measurement or control of fluid flow.
3, product assembly form:
It into a shape and size in two forms.
A, a shape: mounted sensors and switches.
B, size: separation installation sensor and converter, through the connecting cable form flow metering system.
C, in order to adapt to the measurement demands of the different medium, the lining of sensor and electrode materials can have many choices.
Nine, installation requirements:
Electromagnetic flowmeter measurement principle is not dependent on the characteristics of the flow, if the line has some turbulence and vortex in the measurement area (such as elbow, tangential current limiting or upstream of half cut-off valve) has nothing to do with the measurement.If there is a steady state of the eddy current in the measurement zone will affect the stability of measurement and measurement precision, then you should take some measures to stabilize the velocity distribution:
1, increase the length of the straight pipe before and after;
2, using a flow stabilizer;
3, reduce the cross section measurement point.
Ten, the matters needing attention:
1, try to avoid the ferromagnetic objects and equipment with strong electromagnetic field, in order to avoid the magnetic field of magnetic field effect sensor and traffic signals.
2, should be installed in a dry and ventilated place, avoid sharp, environmental temperature should be in 20 ~ + 60 ℃, relative humidity is less than 85%.
Shall have plenty of space around 3, flowmeter, easy to install and maintain.
Eleven, reference flow range:

12, the whole machine and the technology of sensor data:

13, converter technology data:

The lining of the options:

15, import protection flange and the choice of grounding flange ring (or ground) :

16, correct selection:
Instrument selection is very important work in instrumentation, relevant data show that the instrument in two-thirds of faults in the practical application is instrument error caused by selection or wrong installation, please pay special attention to.
1, collect data:
By measurement of body composition;
Minimum flow, maximum flow rate;
The highest working pressure;
The maximum temperature and minimum temperature;
2, range scope confirmation:
General industrial use measured medium velocity of electromagnetic flowmeter with 2 ~ 4 m/s advisable, under special circumstances, the minimum flow rate should not be less than 0.2 m/s, the highest should be not more than 8 m/s.If the medium containing solid particles, commonly used flow rate should be less than 3 m/s, prevent excessive friction lining and electrode;For viscous flow, the velocity can choose more than 2 m/s, larger velocity help eliminate electrode automatic on the effect of viscous material, to improve accuracy of measurement.
Under the condition of the range of Q have been identified, according to the velocity V can be decided to the size of the flow meter diameter D, the range of the values calculated by the next type:
Q = PI D2V / 4
Q: flow (㎡ / h) D: pipe diameter V: velocity (m/h)
Electromagnetic flow meter range of Q should be greater than expected maximum flow, the flow of the normal value in a full scale slightly greater than the flowmeter calibration 50 is advisable.
3, selection table:

17, design selection and ordering information:
1, according to the measurement of fluid medium, correct choose electromagnetic flowmeter.
2, be no corrosive choose normal flow corrosive choose corrosion type.
3, when placing order, please indicate the name of the measured medium, flow rate, pipe size and working pressure, temperature, density, viscosity, and so on and so forth.
4, according to the measuring range of the measurement of body, applications, and choose the right type of specification varieties.