High precision electromagnetic flowmeter
High precision electromagnetic flowmeter is a kind of measuring volume flow tube conductive medium i…
Description：
Products overview:
ZW - LDE seriesHigh precision electromagnetic flowmeterSuitable for all kinds of conductive liquid flow detection, is a necessary instrument in traffic detection project.When conducting liquid flows through the electromagnetic flow time, in the conductor will produce inductive electromotive force.Conducting liquid with velocity V through the magnetic field perpendicular to the flow direction, conductive liquid flow sense if a voltage is proportional to the average flow velocity, and through the cable sent to converter intelligent processing, then the LCD display measurements or converted into standard signal 4 ~ 20 ma output.
Electromagnetic flowmeter is composed of sensors and switches, sensors installed on the measuring pipe, the converter can be connected to the sensor combination together referred to as electromagnetic flowmeter, a size converter is installed within 100 meters of within 30 meters away from the sensor or occasions, are connected by a shielded cable is called separation between type electromagnetic flow meter.Is the main component of the electromagnetic flowmeter sensor: measuring tube, electrode, excitation coil, magnetic yoke iron core and shell.
Second, the working principle:
ZW - LDE seriesHigh precision electromagnetic flowmeter based on Faraday electromagnetic induction principle, with the sounding 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.
Applications:
ZW - LDE seriesHigh precision electromagnetic flowmeter in addition to the general conductive liquid flow can be measured, can also be measured liquid-solid two phase flow, high viscosity fluid and salt, strong acid, strong alkali liquid volume flow.According to the scene of the meet at the same time, also can output 4 ~ 20 ma current signal for records, adjust and control, has been widely used in chemical industry, environmental protection, metallurgy, medicine, paper making, water supply and drainage and other industrial technology and management.
Four, the main features:
1, instrument structure is simple, reliable, have no moving parts, long working life.
2, no closure choke parts, there is no pressure loss and flow 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 adapt to the needs of different medium.
6, with pipeline, plug-in, such as a variety of flow meter type.
7 block, using EEPROM memory, measuring operational data storage safe and reliable protection.
8, integration and separation of two kinds of model.
9, high-definition LCD backlit display.
Five, the technical parameters:
1, precision instrument: pipeline magnitude 0.5, 1.0;Plug in 2.5 on the Richter scale are unlikely.
2, measuring medium: conductivity is greater than 5 mu S/cm of various liquid and liquid-solid two-phase fluid.
3, velocity range: 0.2 ~ 8 m/s.
4, work pressure: 1.6 MPa.
5, environmental temperature: - 40 ℃ ~ + 50 ℃.
6, medium temperature: ptfe lining 180 ℃ or less;Rubber lining material 65 ℃ or less.
7, explosion-proof marks: Exmibd Ⅱ BT4.
8, explosion-proof number: GYB01349.
9, outside magnetic interference: 400 a/m or less.
10, shell protection: integration type: IP65;
In mold: sensor IP68 (5 meters underwater, rubber lining only);Converter IP65.
11, the output signal: 4 ~ 20 ma DC, load resistance Ω 0 ~ 750.
12, communication output: RS485 and CAN bus.
13, electrical connections: M20 x 1.5 internal thread, phi 10 cable hole.
14, power supply voltage: 90 ~ 220 v AC, 24 + / - 10% V.D C.
15, power consumption: 10 or less va.
Six, 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??Single chip microcomputer after the 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.
Seven, 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 use a magnet to produce a uniform magnetic field is constant.The 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.
Eight, installation requirements:
The choice of installation environment
1, should as far as possible away from strong electromagnetic field equipment.Such as big motor, transformer, etc.
2, the installation place should not have a strong vibration, environmental temperature change is not big.
3, easy to install and maintenance.
The choice of the installation position
1, sensors, flow mark on the direction of the measured medium flow and the pipe must be consistent.
2, installation location must ensure that the measuring tube in the book is full of measured medium.
3, and the choice of fluid flow pulse smaller places, which should be far away from the pump and local resistance (valve, elbow, etc.)
4, the measurement of two-phase fluid, should choose is not easy to cause the location of the phase separation.
A negative pressure, avoid installed in a tube of five places.
6, when makes the electrode measured medium, measure the tube inner surface adhesion, scaling, suggest the measuring tube flow velocity of no less than 2 m/s.
At this time can use reducing pipe diameter slightly smaller than the process.For uninterrupted flow in the process piping cleaning electrode and the measuring tube, sensor can be used parallel installations, and cleaning.
The choice of the installation site
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;Valve should be installed in the downstream flow meters.Eight, notable matters of installation:
1, when moving and lifting sensor, should will sling set beside the sensor on both ends of the flange neck position, do not in the measurement, hoisting so as not to damage the lining tube inserted into the pipe to help.
2, before the installation, the sensor electrode with alcohol cotton in carefully erased due to causes such as hand touch the surface of the electrode material grease stain.
3, the inner diameter of the sealing washer when installation should be consistent with the sounding pipe lining inside.
4, must ensure that the terminal box is dry, otherwise the instrument measurement error may result.
Nine, production installation requirements and use:
1, the external environment of requirements:
A, flowmeter should avoid installed in high temperature radiation temperature changes a lot, or by equipment, if must be installed, must be backed by a heat insulation, ventilation measures.
B, flowmeter installation indoors as far as possible, if must be installed in the outdoor, should avoid the rain pouring, water flooded and exposure to the sun, shall be moistureproof and sun protection.
C, flowmeter installation should be avoided in the containing corrosive gas environment, must be installed, ventilation measures shall be required.
D, easy for installation, maintenance, maintenance, and around the meter should be full installation space.
E, flowmeter installation site should avoid to have a strong magnetic field and the strong vibration source, such as the pipeline vibration, bearing of the pipeline in flow meter should be fixed on both sides.
2, the requirement of process pipe
Flowmeter tube of upstream or downstream of the installation points technology has certain requirements, otherwise affect measurement accuracy.
A, the inner diameter of the pipe, the downstream process is the same as the inner diameter of the sensor, and should meet: 0.98 DN D 1.05 or less or less DN (type of DN: sensor inside diameter, D: process pipe diameter)
B, the craft is tube and sensor must be concentric, coaxial deviation should be no greater than 0.05 DN
3, the requirement of the by-pass pipe
In order to facilitate maintenance flow meter, flowmeter by-pass pipe installation, in addition, the polluting fluid and flow meter should be cleaned and fluid can't stop, you must install by-pass pipe.
Ten, notable matters of installation:
1, when moving and lifting sensor, should will sling set beside the sensor on both ends of the flange neck position, do not in the measurement, hoisting so as not to damage the lining tube inserted into the pipe to help.
2, before the installation, the sensor electrode with alcohol cotton in carefully erased due to causes such as hand touch the surface of the electrode material grease stain.
3, the inner diameter of the sealing washer when installation should be consistent with the sounding pipe lining inside.
4, must ensure that the terminal box is dry, otherwise the instrument measurement error may result.
The preparing work before 11, run:
1, put into operation after installation wiring should be checked again before the installation, wiring is correct.(the size)
2, before the bed bottom valve is opened, the sensor after the valve closed, let the sensor with the medium.
3, after the completion of the preparation, upstream of the valve to open the first sensor, then slowly open the downstream of the valve, observe the converter instantaneous flow display should be toward the direction of change, that signal lines in the right direction.Otherwise, will signal A and B connection swap position.(the size)
4, open the sensor before and after the valve, drainage for a few minutes, the gas discharge tube.
5, close the sensor downstream of the valve, then close upstream of the valve, the measured medium is inside the sensor.And then to form a complete set of adjustment.Sensor and converter matching coefficient of zero adjustment and instrument set converter specifications, please read them.
12, main technical data:
1, the whole machine and the technology of sensor data:
Execution standard | JB／T 9248—1999 | ||||
Nominal diameter | 15, 20, 25, 32, 40, 50, 65, 80, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000 | ||||
High velocity | 15m／s | ||||
precision | DNl5～DN600 | Show the value of the: plus or minus 0.3% (velocity of 1 m/s or higher);Plus or minus 3 mm/s < 1 m/s (velocity) | |||
DN700—DN3000 | Plus or minus 0.5% of the value (velocity of 0.8 m/S or higher);Plus or minus 4 mm/s < 0.8 m/s (velocity) | ||||
Fluid conductivity | ≥5uS／cm | ||||
Nominal pressure | 4.0MPa | 1.6MPa | 1.0MPa | 0.6MPa | 6.3、10MPa |
DNl5～DN150 | DNl5～DN600 | DN200～DN1000 | DN700～DN3000 | Special orders | |
The environment temperature | The sensor | - 25 ℃ - 10 to 60 ℃ | |||
Converter and a body | - 10 ℃ - 10 to 60 ℃ | ||||
The lining material | Ptfe, chloroprene rubber, polyurethane, fep (F46), and network PFA | ||||
High fluid temperature | - size | 70 ℃ | |||
The separation type | Poly (chloroprene rubber lining | 80 ℃;120 ℃ (when ordering specify) | |||
Polyurethane lining | 80 ℃ | ||||
Ptfe lining | 100 ℃;150 ℃ (when ordering specify) | ||||
Fep (F46) | |||||
And network PFA | |||||
Signal electrode and the grounding electrode materials | Stainless steel 0 crl8nil2m02ti B, C, hartz hartz alloy alloy, titanium, tantalum, platinum/iridium alloy, stainless steel coated with tungsten carbide | ||||
Electrode institutions | DN300—DN3000 | ||||
Connecting flange material | Carbon steel | ||||
Grounding the flange material | Stainless steel 1 crl8ni9ti | ||||
Import protection flange material | DN65—DNl50 | Stainless steel 1 crl8ni9ti | |||
DN200～DNl600 | Carbon steel stainless steel 10 1 crl8ni9ti | ||||
Enclosure protection | DNl5 ~ DN3000 separation type rubber or polyurethane lining sensor | IP65 or IP68 | |||
Other sensors, bodily form separated type flowmeter and converter | IP65 | ||||
Spacing (separation type) | Converter distance sensor is generally not more than 100 m | ||||
2, converter technology data:
The power supply | communication | 85—265V，45—400Hz |
dc | 11—40V | |
Operation keys and display | touch-tone | Four film button can be set to choose all parameters, can also use a PC (RS232) of converter set programming; 3 rows wide Angle of view, wide temperature, with backlit LCD display; Line 1 shows the flow value; Line 2 show that flow units; Line 3 shows total flow percentage, total quantity of forward, reverse, total difference, alarm, velocity of flow. |
The magnetic key type | The selection of two magnetic key is used to display parameters and reset, use PC (RS232) on converter set programming; 2 rows wide Angle of view, wide temperature, with backlit LCD display: Line 1: the magnetic key choice: display flow percentage, total quantity of forward, reverse, total amount, total difference, alarm, velocity of flow. Line 2: display traffic. | |
Internal integrator | Total forward, reverse and total difference amount. | |
The output signal | One-way analog output | Complete isolation, load 600 d or less.When (20 ma); Cap: 0-21 ma optional, each lmA; Floor: 0-21 ma optional, each 1 ma; Forward and reverse flow output way of programming. |
Two-way analog output | The lower limit for.Or 4 ma, the other with one-way analog output. | |
The bidirectional pulse output | Two lines of the output corresponding to forward and reverse flow, 0 ~ 800 hz frequency, maximum of 1-800 hz optional, each IHz; Square-wave or selected pulse width, pulse width limit selected 2.5 s, every 1 ms; Passive isolation switch output transistor, can absorb 250 ma of current, voltage 35 v. | |
Two-way alarm output | Alarm (programming) high/low flow rate, air traffic control, fault state, positive, and reverse flow, analog outrange, pulse volume range, small pulse signal excision, output polarity optional; With isolation protection switch output transistor, can absorb the current of 250 ma, withstand voltage 35 v. (with pulse output isolation) | |
Digital communications | RS232，RS485，HART | |
3, the choice of the lining:
The lining material | The main performance | Zui high medium temperature | Scope of application | |
- size | The separation type | |||
Ptfe (F4) | Is a kind of plastic, stable chemical performance of boiling hydrochloric acid, sulfuric acid, nitric acid and aqua regia, strong alkali and a variety of organic solvents.Not resistant to high velocity fluid fluorine, oxygen, the oxygen corrosion. | 70 ℃ | 100 ℃ 150 ℃ (special order) | 1, strong corrosive medium such as strong acid, alkali.2, health, type of medium. |
Fep (F46) | With F4, abrasion resistance, resistance to negative pressure ability is higher than the F4. | Same as above | ||
Fluoropolymer and ethylene (Fs) | For maximum temperature was lower than those of ptfe, but the cost is low. | 80 ℃ | ||
Poly (neoprene | 1, has excellent flexibility, high break strength, wear-resisting performance is good.2, generally low concentration acid resistance, alkali, salt medium corrosion, oxidation of medium corrosion resistance. | 80 ℃ 120 ℃ (special order) | Water, sewage and mud pulp weak up to wear and tear. | |
Polyurethane rubber | 1, wear-resisting performance is extremely strong. 2, poor corrosion resistance. | 80 ℃ | Neutral strong wear of slurry, coal slurry and mud | |
4, import protection flange and the choice of grounding flange ring (or ground) :
The flange type | Comfortable with van |
Grounding the flange ring (or ground) | Non-conductors is suitable for pipeline, such as plastic pipe, but has the grounding electrode sensor doesn't need. |
Import protection flange | When the medium has strong wear. |
5, the choice of electrode:
Electrode materials | Corrosion resistance and wear resistance |
Stainless steel 0 crl8nil2m02ti | Used for industrial water, water, sewage with weak corrosive medium, such as applicable to petroleum, chemical, steel and other industrial sectors and, municipal, environmental protection and other fields. |
Hartz alloy B | Below boiling point for all the concentration of hydrochloric acid have good corrosion resistance, resistant to sulfuric acid, phosphoric acid, organic acids and other non chloride acid, alkali, corrosion of non oxidizing salt solution. |
Hartz alloy C | Non oxidizing acid such as nitric acid, mixed acid, or a combination of chromic acid and sulfuric acid medium corrosion, oxidation resistance and salts such as Fe, ",,, Cu "or with other antioxidant corrosion, such as higher than normal temperature hypochlorite solution, the corrosion of the water |
titanium | The sea, all kinds of chloride and hypochlorite, oxidizing acid (including fuming sulfuric acid), organic acid, alkali corrosion.Not a pure resistance reducing acid such as sulfuric acid, hydrochloric acid corrosion, but contains antioxidants such as acid (such as nitric acid, Fc++, Cu++), the corrosion is greatly reduced. |
tantalum | It has excellent corrosion resistance and glass is similar.Besides fuming sulfuric acid, alkali, cut almost ability - chemical medium (including the boiling point of hydrochloric acid, nitric acid and sulfuric acid l below 50 ℃) of the corrosion.In the alkali diao;Corrosion resistant. |
Platinum/titanium alloy | Almost can cut - chemical medium, but does not apply to aqua regia and ammonium salt. |
Stainless steel coated with tungsten carbide | Used for non-corrosive, strong wear medium. |
Note: due to the variety of medium, the corrosion resistance and affected by complex factors such as temperature, concentration, flow velocity and change, so the data in this table is for reference only.Users should choose according to actual situation, should be done when it is necessary to choose the corrosion test of material, such as coupon test. | |
13, 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;
Large flow, small flow;
Z high work pressure;
, z z high temperature low temperature;
2, range scope confirmation:
General industrial use measured medium velocity of electromagnetic flowmeter with 2 ~ 4 m/s advisable, under special circumstances, z low velocity should not be less than 0.2 m/s, high z 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 zui flow value should be greater than expected, the flow of the normal value in a full scale slightly greater than the flowmeter calibration 50 is advisable.
3And the reference flow range:
CAL(mm) | Flow range(m3/h) | CAL(mm) | Flow range(m3/h) |
Phi is 15 | 0.06 ~ 6.36 | Phi 450 | 57.23~5722.65 |
Phi 20 | 0.11~11.3 | Phi 500 | 70.65~7065.00 |
Phi is 25 | 0.18~17.66 | Phi 600 | 101.74~10173.6 |
Phi 40 | 0.45~45.22 | Phi 700 | 138.47~13847.4 |
Phi 50 | 0.71~70.65 | Phi 800 | 180.86~18086.4 |
Phi 65 | 1.19~119.4 | Phi 900 | 228.91~22890.6 |
Phi 80 | 1.81~180.86 | Phi 1000 | 406.94~40694.4 |
Phi 100 | 2.83~282.60 | Phi 1200 | 553.90~55389.6 |
Phi 150 | 6.36~635.85 | Phi 1600 | 723.46~72345.6 |
Phi 200 | 11.3~1130.4 | Phi 1800 | 915.62~91562.4 |
Phi 250 | 17.66~176.25. | Phi 2000 | 1130.4~113040.00 |
Phi 300 | 25.43~2543.40 | Phi 2200 | 1367.78~136778.4 |
Phi 350 | 34.62~3461.85 | Phi 2400 | 1627.78~162777.6 |
Phi 400 | 45.22~4521.6 | Phi 2600 | 1910.38~191037.6 |
14, selection of coding:
specifications | Pipe size | Wei measurement and control of the () material: nodular cast iron and stainless steel | ||||
ZW-LDE/B | 15-2600 | |||||
Code name | Electrode materials | |||||
K1 | 316L | |||||
K2 | HB | |||||
K3 | HC | |||||
K4 | titanium | |||||
K5 | tantalum | |||||
K6 | Platinum alloy | |||||
K7 | Stainless steel coating Coated tungsten carbide | |||||
Code name | Lining material | |||||
C1 | teflonF4 | |||||
C2 | fepF46 | |||||
C3 | Poly fluoro ethyleneFS | |||||
C4 | Poly (butyl rubber | |||||
C5 | Polyurethane rubber | |||||
Code name | function | |||||
E1 | 0.3level | |||||
E2 | 0.5level | |||||
E3 | 1level | |||||
F1 | 4－20Madc,load750 or less Ω | |||||
F2 | 0-3khz,5vActive, variable pulse width, the output high frequency effectively | |||||
F3 | RS485interface | |||||
T1 | The normal temperature type | |||||
T2 | High temperature type | |||||
T3 | Ultra high temperature type | |||||
P1 | 1．0MPa | |||||
P2 | 1．6MPa | |||||
P3 | 4．0MPa | |||||
P4 | 16MPa | |||||
D1 | 220VAC±10% | |||||
D2 | 24VDC±10% | |||||
D3 | Lithium battery type | |||||
J1 | A body structure | |||||
J2 | Points body structure | |||||
J3 | Explosion-proof one body structure | |||||
15, design selection and ordering information:
1, the measured medium: name, composition, status, electrical conductivity and electrical conductivity;
2, working temperature (℃);
3, work pressure (Mpa);
4, the pipe diameter (DN), the smallest, normal, scope of quantity (m3 / h);
5, corrosion resistance, wear resistance, whether there is a negative pressure;
6, installation requirements and the environment: a body or fission, signal output, communications, power supply;
7, installation environment: protection grade and explosion-proof requirements.
After-sales service commitment:
1, from the date of signing of the contract, I in the way provided for products of the company offers free maintenance and maintenance service, commitment to lifelong maintenance service;
2, jiangsu wei measurement and control instrument co., LTD. Sales manager will be in regular contact with customers, understand the usage of products, and solve the problems of the customers to use in the process of produce, free of charge to provide technical support;
3 the man-made damage is found, the warranty period, our company is responsible for the maintenance, and the resulting maintenance fee;
4, product quality problems or are not satisfied with product, the user can choose unconditional return, wei tt&c don't charge any fees, appear quality problem, bear the freight back and forth.
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