【 Weak current College 】 resistor designation, resistors classification, main characteristics of the parameters, the resistance of the marks, common resistors, resistor 】

Resistance

Conductors on current impediment that resistance, expressed by the symbol R units of ohm, kilohms, megohm, respectively Ω, k Ω Ω, M.
First, the resistance of a model named method:
Homemade resistors model consists of four components (does not apply in sensitive resistor)
Part i: the primary that letter that represents the product name. If r = resistance, W represents a potentiometer.
Part II: material, letter, indicating that the resistance of what material composition, T-carbon film, H-synthetic organic carbon, black, S-N-inorganic solid, J-metal film, Y-C-nitride film and deposition films, I-glass glaze film, X-wire wound.
Part three: general classification, a number, the individual type of letter that represents the type of product. 1-normal, normal, 2-3-UHF, 4-high-temperature-resistance, 5-, 6-precision, high precision, 7-8-9-special high pressure, and G-high power, T-adjustable.
Fourth part: serial number, a number that represents the class of different varieties to differentiate the product dimension, and performance indicators, etc.
For example: R T 1 1-ordinary carbon film resistors a1} 2 resistors classification
1. wire-wound resistors: General-purpose wire wound resistors, precision wire wound resistors, power wire wound resistors, RF wire wound resistors.
2 film resistor: carbon film resistors, synthesis of carbon film resistors, resistor metal film, metal oxide film resistors, chemical deposition film resistors, glass glaze film resistors, metal nitride film resistors.
3. solid resistor: inorganic synthesis of solid carbon resistors, organic solid carbon resistor.
4. sensitive resistor: pressure-sensitive resistors, Thermistors, photosensitive, force sensitive resistor, gas sensing resistors, humidity sensitive resistor. III. main characteristics
1. nominal resistance: resistor above marked resistance.
2, allows error: nominal resistance and the actual resistance of difference with nominal resistance ratio percentage that deviation, it indicates that the resistance resistors for accuracy.
Permissible error and precision grade correspondence: ± 0.5%-0.05, ± 1%-0.1 (or 00), ± 2%-0.2 (or 0), ± 5%-Ⅰ, Ⅱ ± 10%-20%, ±-grade ⅲ
3. rated power: at normal atmospheric pressure 90-106.6KPa and environment temperature:-55 ° c ~ + 70 ° c, the resistors long-term work the allowed maximum power dissipation.
Wire-wound resistors rated power series (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 4, 8, 10, 16, 25, 40, 50, 75, 100, 150, 250, 500
Nonlinear wound resistors rated power series (W): 1/20, 1/8, 1/4, 1/2, 1, 2, 5, 10, 25, 50, 100
4. rated voltage: from resistance and rated power conversion out of voltage.
5, maximum working voltage: maximum continuous operating voltage. When working in low atmospheric pressure, maximum operating voltage is low.
6. temperature coefficient: temperature 1 ° c per change resulting from the resistance values of relative change. Temperature coefficient of resistance is smaller, the better stability. Resistance with temperature but increased for positive temperature coefficient, and conversely a negative temperature coefficient.
7, aging coefficient: resistors in long-term load rating, the resistance percentages relative change, it is the length of the resistors life.
8, voltage coefficient: the voltage range, the voltage every variation 1 volt, the amount of relative change resistors.
9. noise: from resistors of irregular voltage fluctuations, including thermal noise and current noise, thermal noise is irregular because the conductor internal electronic freedom movement, the conductor any two points in irregular changes. 4. the resistance of the marking methods for resistors
1. direct standard method: the number and unit symbols in resistor surface marked resistance, its allowable error of direct use of percentage that if the resistance is not note deviation, are ± 20%.
2, letter symbols: symbol text with Arabic numbers and a combination of both to represent nominal resistance, its allowable deviation also used text symbol. Symbol preceding digit integer resistance, the numbers following the order represents the first decimal resistance and the resistance in the second decimal.
Allows error text symbols
Text symbol D F G M J K
Tolerances ± 0.5% ± 1% ± 2% ± 5% ± 10% ± 20%
3. digital method: resistors with three digital represents the nominal value of the flag. Digital from left to right, first and second place as a valid value, the third position for the index, i.e. the number of zero bits '. Deviation usually uses the text symbol.
4, color standard method: the belt of a different color, or point mark in resistor surface nominal resistance and tolerance. Most foreign resistance using color-coding method.
Black-, brown-red-1, 2, 3, orange-yellow-green-4, 5, blue-violet-6, 7, ash-8, white-9, Gold-± 5%, silver-± 10%, 20% transparent colorless-±
When the resistance for the fourth time, the last part will be gold or silver, the first two digits of the digits, the first three digits of the number of fourth powers, as errors. When the resistance of five rings, the last ring and ring distance larger front. First three digits of the digits, the first four digits of the number of powers, the fifth digits of the deviation. 5. common resistors
1, potentiometer
Potentiometer is an electromechanical components, he brushes in resistance on the slide, and brush displacement into certain relations of output voltage.
1.1 synthesis carbon film potentiometer
Resistance of the body is lapped black carbon, graphite, quartz and other materials for coating to the substrate, the process is simple, is the most widely potentiometer. Features a resolution of high wear resistance, long service life. The disadvantage is that current noise, nonlinearOf moisture resistance and the resistance of the poor stability.
1.2 organic solid potentiometer
Organic solid potentiometeris a new type potentiometers, it is a method of heating plastic pressure, resistance to organic powder pressure in the notches on the insulator. Organic solid potentiometers and carbon film resistor has a good heat resistance, high power, high reliability, good wear resistance. But the temperature coefficient of large, dynamic noise, poor resistance to humidity, complex manufacturing process, the resistance of the poor precision. In miniaturization, high reliability, high wear resistance of electronic equipment, as well as AC, DC circuit used for the adjustment of voltage and current.
1.3 metal glass uranium potentiometer
Use screen printing method in accordance with certain graphics, metallic glass uranium resistor paste coating in ceramic substrate, high-temperature sintering. Characteristics: wide resistance range, good heat resistance, overload capacity, high tide, wear, etc., are all very well, is very promising potentiometer varieties, the disadvantage is that contact resistance and current noise.
1.4 wound potentiometer
Wound potentiometer is Kang copper wire or NI-CR alloy wire as resistance, and turned it around in insulated skeleton. Wound potentiometer is characterized by low contact resistance and high precision, low temperature coefficient, the drawback is to distinguish the resistance is low, low, high-frequency characteristics of the poor. Mainly used as a divider, rheostat, instruments and work in the zero point.
1.5 metal film resistor
Metal membrane potentiometer resistors body can consist of alloy film, metal oxide film, metal foil, respectively. Features high resolution power, heat-resistant, temperature coefficient is small, dynamic noise small, smooth and good.
1.6 conductive plastic potentiometers
Use special techniques to DAP (phthalate dilute acrylic ester) resistor paste clad in insulated body, heating aggregates into resistance membrane, or DAP resistance powder thermoplastic insulating substrate of pressure in theform of a solid Groove as resistance. Characteristics: smooth, high power superior wear resistance, long life, dynamic noise small, high reliability, excellent resistance to chemical corrosion. For cosmic device, missiles, aircraft and radar antennas of servo system, etc.
1.7 band switch potentiometer
A rotary switch potentiometer, push-pull switch potentiometer, push switch type potentiometers
1.8 pre-adjustable potentiometers
Pre-adjustable potentiometers in circuit, once debugging is good, with wax seal adjustment positions, under normal circumstances no longer regulated.
1.9 straight sliding potentiometer
Use straight sliding way to change the resistance value.
1.10 dual-attached potentiometers
Different shaft dual-attached potentiometers and coaxial dual-attached potentiometers
1.11 contactless potentiometer
Non-contact potentiometer eliminates mechanical contact, long life, high reliability, opto-electronic potentiometer, magnetic-potentiometers, etc.
2. solid carbon resistors
Carbonaceous particles Chuang conductivity material, filler and Binder mixture made of an entity of the resistor.
Characteristics: low prices, but their resistance errors, noise voltage are large, poor stability, is now less used.
3. wound resistors
With high resistance alloy wire wound in insulated skeleton made of coated with heat resistant outside glazing insulation or varnished.
Winding resistance with low temperature resistance coefficient, high precision, good stability, heat resistance and corrosion resistance, mainly used for high-power resistors do precision, the disadvantage is that high-frequency performance, the time constant.
4, thin film resistors
With evaporation method will necessarily resistivity material evaporation from the surface of insulation materials. The major as follows:
4.1 carbon film resistors
The crystalline carbon deposition in ceramic rods skeleton. Carbon film resistors with low cost, stable performance, wide resistance range, temperature coefficient and a low voltage coefficient, is the most widely resistor.
4.2 metal film resistors.
By vacuum evaporation method alloy evaporation from the surface of ceramic rods skeleton.
Metal film resistors than carbon film resistors for high precision, good stability, low noise, temperature coefficient. In instrumentation and communications equipment for use in large quantities.
4.3 metal oxide film resistors
In insulated rod on a layer of metal oxides. Because of its own that is oxides, high temperature stability, resistance to impact, the load capacity.
4.4 synthetic membrane resistance
The conductive composite suspensions coated in the substrate, thus also called paint film resistors.
Because of its conductive layer rendering granular structure, its low noise, precision, mainly with his manufacturing high pressure, high resistance, small resistor.
5, metal glass uranium resistors
The metal powder and mixed uranium powder glass, using screen printing method in the substrate.
Resistance to humidity, high temperature, low temperature coefficient, mainly used in thick film circuit.
6, SMT SMD resistors
Chip resistors are metal glass uranium one form of resistance, his resistance is high reliability of Ruthenium series glass uranium materials after high temperature sintering, electrode with silver-palladium alloy pastes. Small size, high precision, good stability, since it is a chip components, high-frequency performance.
7, sensitive resistor
Sensitive resistance refers to the device properties on temperature, humidity, voltage, light, gas, pressure effects of magnetic field, sensitive resistor.
Sensitive resistor symbol is the symbol of resistance in common with a slash, in and to the type of callout sensitive resistor, such as: t. V.
7.1, varistor
There are silicon carbide and zinc oxide varistor, zinc oxide has more characteristics.
7.2, humidity resistance
The humidity level, electrodes, insulators, humidity resistance include lithium humidity resistance, moisture resistance, carbon oxide humidity resistance. Licl humidity resistance with increased humidity and resistance to reduce the scope for testing, shortcomings, properties of repetitive, affected by temperature. Carbon humidity resistance and low-temperature sensitivity disadvantages, resistance temperature high-impact, the ageing behaviour, less use.
Oxide humidity resistance performance superior, long-term use, small, resistance temperature and humidity variation is linear. A tin oxide, nickel-iron salts, and other materials.
7.3,-
PhotosensitiveResistance is the conductivity as light t overload of changes of electronic components, when a substance is light, carrier concentration increase thereby increasing electrical conductivity, photoconductive effect.
7.4, gas resistance
Take advantage of some semiconductor absorption occurs after a gas redox reactions, the main ingredient is metal oxides, main varieties are: metal oxide gas resistance, composite oxide gas gas sensing resistor resistor, ceramics, etc.
7.5, force sensitive resistor
Force sensitive resistor is a kind of resistance with pressure changes in resistance, overseas known as piezoelectric resistor. The so-called pressure resistance effect that semiconductor materials resistivity with mechanical stress change effect. Formed by the torque meter, semiconductor microphone, pressure sensor, etc. Main varieties are Silicon force sensitive resistor, selenium and tellurium metal force sensitive resistor, relatively speaking, alloy resistor has a higher sensitivity.

【 Weak current College 】 shielding technology profile 】

Shielding is on two space area of isolation between the metal to control electric, magnetic and electromagnetic waves from one zone to another zone of induction and radiation. Specifically, it is a shield to components, circuits, components cable, or an entire system of sources of interference, avoid interference surrounded by electromagnetic field to diffusion; Shield will receive circuits, equipment or system surrounded by external electromagnetic fields prevent them. Because the shield from the wires, cables, components, circuit or system, and other external interference electromagnetic waves and internal electromagnetic waves are absorbed energy play (Eddy current loss), reflective energy (electromagnetic wave shield interface reflection on) and offset the energy (Electromagnetic induction in the shield on the reverse of electromagnetic field, electromagnetic interference may be offset by some), so the shield with reduced interference function.

(1) when the interference of the higher frequency electromagnetic field, the use of low resistivity of metallic materials in the Vortex, formation of external electromagnetic radiation neutralize effect, so as to achieve the shielding effect.

(2) when the interference electromagnetic waves of frequencies lower, to adopt high permeability rate of material, so that the lines limited to shield itself, prevent the spread to the shield of space.

(3) in some instances, if the requirements for high-frequency and low frequency electromagnetic fields has a good shielding effect, often using different metallic materials composition of multi-layered shield.

Many people don't understand the principle of electromagnetic shielding, think as long as a metal box, and then drag the box grounding, is able to play the role of electromagnetic shielding. In this concept under the guidance of the result is fail. Because, electromagnetic shielding and shield ground or not and there is no relationship. Realimpact shield shielding effectiveness of only two factors: one is the shield is conductive surface must be contiguous, and one cannot be directly penetrate the shield of the conductor. Shield on a lot of conductive points, the main one is the shield combination of different parts of the form of non-conductive crevice. These non-conductive crevice produces electromagnetic leaks, as containers of fluid from the slit on the leak. This leak of a method is to fill in the gaps and eliminate the conductive elastic material is not conductive. This is like in fluid container gaps filled rubber of truth. This flexible conductive fill material is magnetic gasket.

In many documents in electromagnetic shield compared to a liquid seal container only when using conductive elastic material will crack sealing to leak levels to prevent electromagnetic leaks. In fact this is inaccurate. Because gaps or voids will leak the electromagnetic wave, depends on the gap or opening relative to the size of electromagnetic wavelength. When the wave of long term greater than open size, and no obvious leaks. Therefore, when a disturbance of the frequency is high, then the shorter wavelength, it is necessary to use magnetic gasket. Specifically, when a disturbance frequency over time, we should consider the 10MHz uses electromagnetic sealing gasket. Where there is flexibility and conductive good material can be used as a magnetic gasket. In accordance with the principle of the manufacture of magnetic gasket:

Conductive rubber: silicone rubber is filled with a share of 70 to 80 per cent of the weight of metal particles, such as silver, copper, aluminum, silver-coated copper powder, silver-coated aluminium, silver-coated glass balls, etc. This kind of material preserved part of the characteristics of silicone rubber good elasticity, while with good electrical conductivity.

Metal braid: beryllium copper wire, monel wire or stainless steel wire braided into tubular long bar, muchlike shielded cable shielding layer. But it's woven method and the cable shield, the cable shield is compiled with multiple wires, and shield liner is made of a thread. Make a figuratively, just like the sweater sleeve. In order to increase the elasticity of metal mesh, sometimes in network management include rubber core.

Finger Reed: beryllium copper made of Reed, has good flexibility and high electrical conductivity. Conductivity and elastic.

Multiple conductive rubber: consists of two layers of rubber, and strata is ordinary silicone rubber, rubber outer is electrically conductive. This material to overcome the traditional poor conductive rubber elastic shortcomings rubber elasticity to embody. It works somewhat like with rubber-metal wire mesh.

Select use what kind of electromagnetic gasket to consider four factors: shielding effectiveness requirements, there are no environmental sealing requirements, installation requirements, cost structures. Shielded by mechanism can be divided into electric shield, magnetic shielding and electromagnetic shielding.

1 electric shielding
【 Shield mechanism 】: electric field induction as distributed capacitance coupled between.
【 Design 】:
A, shielding plate to near protected as well, and the grounding shield plate must be good!!!
B, shielding plate shape on the shielding effectiveness of significant impact. Fully enclosed metal box of the best, but works very hard to do!
C, shielding plate materials to good conductor, but no requirements for thickness, as long as you have enough strength to.

2 magnetic field shielding
Magnetic shielding typically refers to DC or low frequency magnetic field shield, its effect than electric shielding and electromagnetic field shielding to the poor.
【 Shield mechanism 】: mainly rely on high-TC superconducting magnetic materials with low resistance, magnetic flux plays a role of tapped, makes the internal magnetic field shield is greatly diminished.
【 Design 】:
A, adopt high magnetic materials such as Permalloy;
B, increase the thickness of the shield;
None of the above is to reduce the shielding of magnetic resistance;
C, masked objects do not cause immediately shield location to minimize by masked objects in flux;
D, note the shield structure design, where the seams, ventilation air may increase the shield of reluctance, thereby reducing the shielding effect.
E, for strong magnetic field shielding can be doubleMagnetic shield structure.
On to the external magnetic field shield, shield hard outer Select saturation of materials such as silicon steel; internal can be selected easily reached saturation of high permeability material, such as Permalloy, etc. Conversely, if you want to shield the internal magnetic field, then the material order to over. During the installation of a two-layer shield inside and outside, it is necessary to pay attention to their insulation. When no grounding requirements, supporting insulation materials made available. If you need ground, can choose non-ferromagnetic materials (such as copper and aluminum) do support pieces.

3 electromagnetic field shielding
Electromagnetic shielding is the use of shield prevent electromagnetic fields in the space-borne a measure.
【 Electromagnetic field shielding mechanism 】:
A, when electromagnetic waves reach the shield surface, due to the air and metal interface on impedance discontinuity, the incident wave reflex. This reflection does not require shielding material must have a certain thickness, it only requires interface on the discontinuity;
B, no surface reflection off into the shield of energy in the body and forward transmission process, masked material attenuation. It is the so-called absorption;
C, not yet in the shield attenuation off surplus energy to the material of another surface, encounter metal-air resistance is not continuous interface, will form a reflection, and again returnedto shield the body. This reflection on the two metal interface may have multiple reflection.

In short, electromagnetic shield attenuation of electromagnetic is based on the reflection of electromagnetic waves and electromagnetic wave absorption. 【 Absorption loss 】 different materials, different material thickness for electromagnetic wave absorption effect is different. According to the material absorption loss column chart.
【 Reflection loss 】 is divided into three categories: low-impedance electric field, magnetic field, high impedance, plane wave field.
Which low-impedance magnetic field and high-impedance electric field reflection loss column chart calculation methods are the same, and the frequency of metal materials, and the emitter to the shield of distance.
For plane-wave, wave impedance is a constant, and the emitter to shield regardless of the distance, in nomogram of simply connect metal material and the interest rate you can find out at this time of reflection loss values.

4 practical electromagnetic shield
【 Structure material 】
A, apply to the floor and the enclosure of the materials most are good conductors, such as copper, aluminium, etc, you can shield shielding electric field, the main mechanism is reflected signals instead of absorption.
B, on magnetic field shielding need ferromagnetic material, such as high-permeability alloys and iron. The main absorption mechanism of shielding is instead of reflection.
C, in strong electromagnetic environment, requested materials can shield electric and magnetic fields two constituents, therefore need to structure the ferromagnetic material on intact. Shielding efficiency directly affected by material thickness as well as lap and grounding method is good or bad.
D, for plastic shell, is in its wall spraying shield, or in the steam plastic mixed with metal fiber.

Must minimize structure of electrical discontinuity in order to control the plate and shell access to the leakage radiation. Increase gap shielding effectiveness of structural measures including increased the gap depth, reducing the gap length, add in the combination of surface conductive gasket, seams coloured conductive coatings, shorten the distance between the screws.

【 Lap 】
A, in the case of each floor and a crack and discontinuity to best possible lap. The worst power lap on the shell of shielding effectiveness plays a decisive role.
B, guarantee seams metal to metal contact, to prevent the leakage of electromagnetic energy and radiation.
C, where possible, joint should be welded. In restricted circumstances, available spot welding, riveting and Xiao spacing of screws to fixed.
D, without conductive gasket, screw spacing should normally be less than the maximum operating frequency of 1%, at least not greater than 1/20 wavelength.
E, with screw or rivet for lap time, first in the middle of a good lap joints, and then gradually to extend the ends to prevent bending metal surface.
F, guarantee fastening methods have sufficient pressure to deformation stress, shock, vibration, maintain contact with the surface.
G, the unevenness of the place, or on a removable Panel and other places, you must use conductive gasket or finger spring material.
H, select high conductivity and elastic cushioning. Select the pad combined premises to consider when using frequency.
I, select hard pad made of ductile material to cut any metal surface.
J, guaranteed with cushioning material with metal surface does not have any non-conductive layer of protection.
K, when you need an active contact with finger pressure spring, and it is necessary to pay attention to maintain flexibility means spring pressure.
L, conductive rubber gaskets used in aluminum metal surface, it is necessary to pay attention to the role, electro-chemical corrosion. Sterling Silver fillings of rubber or monel linear pad will appear the most serious of electrochemical corrosion. Silver plated aluminium packing of conductive rubber is salt environment for aluminium metal with the best cushioning material surface.

The following are ranked according to priority range of liners.

1 metal RF padding nets easily deformation, pressure 1.4kg/cm, attenuation as 54db.
Data show that the frequency is low attenuation Max. For permanent seal better, not suitable for open and close panels.

2 copper plating alloy has high conductivity and good corrosion resistance.
Good elasticity, the most suitable for and active panel. Can be made into a bar, spiral and jagged surface. Attenuation as 100db.

3 conductive rubber applies to just name a connection and a small amount of screws.
Realization of water vapor sealing and electrical seal by the 48-hour 1500 ° c, the body after agingResistivity is 10 ~/cm 20m ω (max). Deformation of limit values for 25 per cent. Data show that the frequency is high attenuation as a maximum.

4 conductive inner fabric in foam on a piece of silver plated braid, forming a soft cushion, occupies most of the loose space, mainly civilian, suitable for foam gasket Cabinet and door panel.

【 Penetrating and opening 】

A, it is necessary to pay attention to as the cable through the chassis so that the overall reduction of shielding effectiveness. Typical wire is not filtering through the shield, the shielding effectiveness over lowering 30db.
B, power cables into the enclosure, all through the filter cartridge. Filter's input should be put out to the outer shielding casing; if the structure is not suitable for wearing out the filter shell, power cables into the enclosure out specifically for the filter settings of a compartment.
C, signal line, control line into/in and out of the enclosure, through the appropriate filter. With filter insert the needle of multi-core connectors suitable for such use.
D, through shield metal control axis, we should use metal touch tablet,ground nut or RF liner grounded. You can also do not have a grounded metal shaft, and other axis through the waveguide cutoff frequency ratio frequency high Park tube to do control the shaft.
E, attention must be paid within the due wave guided hole through metal shaft or wire shielding effectiveness is seriously degraded.
F, when asked to use the insulation of the metal control axis, the available short invisible control axis, not regulation, nut or metal gasket elasticity install cardboard cover.
G, fuse, Jack, etc. with metal caps.
H, conductive gaskets and washers, nuts, etc. implement button child switch leakage installed.
I, the shield, ventilation and strength requirements of high quality not demanding, with honeycomb plate shield vents, the best way to keep the lines of welded connections, preventing leakage.
J, as in indicator, monitor followed by shielding, and on all lead through capacitor filter used.
K, not from the rear shield indicator/display and pairs leader filtering use and continuous connection of metal casing or conductive glass shield indicator/in front of the monitor. Wafer wire shielding glass, while maintaining reasonable transmittance, for 30 ~ 1000m of shielding effectiveness of up to 50 ~ 110db. In transparent plastic or glass coating of transparent conductive film, its shielding effect is usually not greater than 20db. But the latter eliminates observation Windows on electrostatic accumulation, commonly used in the instrument.

College】 【weak】 VOD video on demand technology..

<br> VOD video on demand technology <BR> VOD (Video on Demand) is a short video on demand technology, also known as interactive television on-demand system, which means users need to play according to the corresponding video, to fundamentally change the user .Over the past lack of passive TV viewing. .When you turn on the TV, you can not see ads for a program does not hurry, always want to watch content on demand directly, as if just playing into his home VCR or VCD machines in a new film, but you do not .need to purchase a tape or VCD disc, do not need VCR or VCD machine. .This is the information technology to bring your dream, it will be video programming through a multimedia network in accordance with the wishes of individuals to every household. .Looking at the application of broadband networks, VOD Most people live close to, but also the largest of its technical difficulty. .Take the words of China Telecom is the high road with, it is necessary to run a car, VOD broadband multimedia network application is the most eye-catching car. .VOD technology can be applied not only to broadband networks in telecom, but also can be used in LAN area and cable broadband networks. .Today, intelligent community in the construction process, the computer network cabling has become the essential part of the user can plot a computer, TV (with set-top box), etc. to achieve VOD video on demand applications, enriching the cultural life of the people; cable through .two-way transformation, allowing the majority of TV users to broadcast video cable network. .As a VOD system consists of three parts: server server side system consists of video servers, file management server, internal communications subsystems and network interface. .File management server is mainly responsible for customer information management, billing, video materials, finishing and security missions. .Completion of internal communication subsystem main information transfer between servers, back-visual materials and data exchange. .Main achievement of the network interface for data exchange with external networks and providing user access to the interface. .Mainly by the video server storage devices, high-speed cache and control management unit, whose goal is to achieve data compression and storage media, and according to media requests for information retrieval and transmission. .Video server and data server has many traditional significantly different, need to increase the number of dedicated hardware and software features equipment to support the special needs of the business. .For example: media, data retrieval, real-time information flow and information transfer the encryption and decryption. .For the interactive VOD systems, server systems also need to implement the processing of user requests in real time, access permissions control, VCR (Video Cassette Recorder) functions (eg, fast forward, pause, rewind, etc.) of the simulation. .Network systems, including network backbone network and local network in two parts. .Because it is responsible for real-time transmission of video information stream, so the continuous media web services that affect crucial parts of the system performance. .Meanwhile, the media service system, the network portion of the huge investment and therefore should not only be considered in the design of the current high-bandwidth media applications on demand, but also the future development needs and backward compatibility. .Currently, the system can be used to establish such a service network of the main physical medium is: CATV (Cable TV), coaxial cable, fiber optic and twisted pair. .The network technology used in the main are: Fast Ethernet, FDDI and ATM technologies. .Currently the client system, according to the different functional requirements and application scenarios, there are three VOD systems: NVOD, TVOD, IVOD. .NVOD (Near-Video-On-Demand), may be called near-style on-demand television. .This on-demand television way: multiple video streams in turn start a certain time interval to send the same content. .For example, a dozen video streams every ten minutes to send the same to start a two-hour television programs. .If you want to watch this television program might need to wait, but the longest no more than ten minutes, they would choose their nearest the starting point for some time to watch. .In this way, a video stream may be for many users to share. .TVOD (True Video-On-Demand), called the true on-demand television, it really supports the point that place. .When the user requests the video server will immediately send the user to the video content. .If another user made the same demand, video server will immediately transfer him to start another video stream the same content. .However, once the video stream to start playing, we should continue to play continuously until the end. .In this way, each video transfer for a customer service. .IVOD (Interactive Video-On-Demand), known as the interactive on-demand television. .Than the first two methods are much improved. .It not only can support the point that release, but also allows the user interactive control of video stream. .At this point, the user can operate like a traditional VCR, as to achieve the program play, pause, rewind, fast forward and automatic search. .Only use the appropriate terminal device, the user can with a service or service provider to contact and interoperability. .In VOD system, the need TV and set-top boxes (Set-top Box), in some special systems, may also need a large capacity hard disk with a computer to store video files from the video server. .Client system, in addition to involving the appropriate hardware, but also with related software. .For example, to meet the needs of the user's multimedia interaction, client systems must be modified interface. .In addition, during the continuous media playback, media stream buffer management, audio and video data, synchronization, network outages and problems of coordination studio interruption need to be fully considered. .Although very attractive VOD service can be seen, but its implementation technology is not a "easy nut to crack." .But as the network technology, computer technology, storage technology, the rapid development of VOD customers to enjoy the full fun of the day is not far off. .By that time, on-demand users will operate the remote control, push the button, you can watch and enjoy all wishes come true in their favorite programs, and are free to adjust the screening schedule, speed and so on. .The emergence of VOD makes TV becomes a random access to information to the media, more like a book or a newspaper, you can browse, you can adjust, no longer restricted to a particular time, date, and fixed limit program .. .Although, VOD initial appearance of the user in order to better meet the needs of independent video to watch, but as the VOD technology continues to progress, and its wide range of applications of popular culture and business model will have a strong influence. .VOD can not only provide end users with a variety of media, information flow, to expand people's access to information to enrich people's spiritual life; but also in hospitals, hotels, airplanes and other places of entertainment, the company's staff training, long-distance market research, company .areas of the advertising business will be gradually filled with VOD technology, new applications. .<BR>.

Weak current College】 【buy video conference system what factors to consider when】.

Video conferencing system is now used more widely, optional video conferencing products more and more, then our how to choose the right video conferencing system, let's briefly describes video conference system guide:
1. the system should be secure, stable, reliable operation
Real-time video system is a very strong system, while propagating information also has the very high demand, so in these secrets to organize meetings, secure, stable, reliable operation of the most basic requirement.
Security refers to the organizers of the meeting of the Conference have the highest administrative authority without the approval of the meeting organizer, any user will be logged, including system administrators, administrators can easily see any personnel participating in the meeting information, thereby ensuring that meeting information does leakage;
Stability is a Conference is a continuous process, the Conference has its own program, any intermediate disturbance will directly affect the quality of the Conference, so called video system should have high stability in order to guarantee full Conference;
Reliable means the system is a complex multimedia, intermediate technical level range has a large number of management, combined with the enormous space span, remote, including equipment and personnel to operate using easily manage and control, so the system anti-interference ability and incitement Kang equity between lame sword Commission investigation into climbing gear to tranche V A?
2. the system should have excellent quality
Impact Conference staff interest and attention of two factors: one is the environment to the extent of human vision, environmental infection can stimulate participation of emotions, or lecture with passion, or lecture with enthusiasm; another is the sound level of attracting good quality voice can increase participation in the Conference staff, or speech seriously, or listen carefully. But video conferencing with traditional face-to-face meetings is essentially the difference, to achieve the effect, in addition to the traditional meeting of the Conference room lighting, audio enhancement and related equipment quality, also require video system has a very high quality and guarantee that the image screen clear translucent, sound clarity clean spread to cause all persons participating in the meeting's attention to the purpose of the meeting.
A large amount of data that a person's overall attention 70% come from image to attract, 30% comes from sound, thus, enhance the image of fun and the voice of the beautiful nature, is a measure of the level of quality of video system. In order to strengthen the confidence of the speaker, improve their language, video system should be able to add multiple pictures at the same venue in the speaker before the eyes of many people jump in front of the lens, to inspire speaker's performance, and performance of its content. At the same time be able to add multiple pictures at the same venue in hearing, sight, provides fresh fun lenses, plus high-quality sound, we can grab the listener's attention, and the expulsion of the Conference for comprehensiveness of snooze.
3. the system should have the complete features
As the name implies, the video system is to provide video and audio services system, it is not only the tasks you want to have video conferencing, and more is to have other audio services; thus, it has video conferencing, video instruction, VOD, video broadcast or rebroadcast, remote TV on-demand, remote video phone, remote video surveillance, and other service functions is a real video system.
4. the system should have a strong environmental adaptability
Video systems are designed for long distance space requirements, data communication conditions determine the video system work is good or bad. Co-ordinate computer network resources, reasonable arrangement of resources use plan, is the performance of today's civilization, no sector or enterprise with a dedicated data channel for video system to provide services, visible video system construction is actually a way to "borrow" concept, it is built on the computer sharing network. Because video system requirements are strict, continuous and real-time data transfer, and in computer networks, data transmission is ever, for video system, on the one hand, require excellent voice tone, voice absolutely continuous, image more clear, no mosaic and anomalies; on the other hand require audio packets cannot be too large to guarantee that the data should be transmitted in real time, such as the relationship between the opposition and unity, to the video system offers high standards, so the video system on the computer network of adaptive capacity becomes extremely important, in addition to sophisticated technical means, of their own anti-jamming ability is strong than the General system, to meet peak network data transmission, particularly when encountering a virus interference, should absolutely guarantee small audio signal data real-time continuous priority transfers instead of large video signal data transfer can be continuous or discontinuous transmission packet loss, but need to have the related processing technology guarantees no mosaic and anomalies.
In addition, because the IP network and the rapid development of audio-video equipment, various access networks and devices driver layer out of the infinite, so the system adapts to a variety of network access and use of more audio and video equipment, as well as video system adaptation to the environment as an important indicator of ability.
5. the system should have a very good compatibility
Video system to have a good compatibility, in addition to its own version upgrade compatibility and product characteristics, the wandering and other brand products for audio signal interchange ability, can guarantee users not wasted the past use of imaging resource and the largest in the hands of the rationalized use of other brands product resources.
6. the system should facilitate the management and use
Video system is a shared platform, it should be a public, easy to use tool, not only for professional and technical personnel to use the system, so the system's ease of use is the product direction of development. At the same time, the system should provide a full range of management functions, not only in the foreground for conference management and data requests, but also in the background to the meeting and network data traffic management and monitoring, to be called a good video system products.

【 Weak current College 】 achieve high-efficiency automatic routing of PCB design techniques and elements 】

Although now the EDA tool is very powerful, but with the PCB size requirements are smaller, higher density devices, PCB design of difficulty is not small. How to implement a PCB layout pass rate high as well as reduce design time? this article describes the PCB layout, the layout and wiring design techniques and elements. PCB design time now shorter and shorter, smaller and board space, higher density devices, extremely demanding layout rules and the large size of the components allows designers to work more difficult. In order to solve design problems, and accelerate product listing, now many manufacturers tend to use EDA tools for PCB design. But dedicated EDA tool does not produce the desired results, also not 100% pass rate of cloth, and messy, and often need to spend a lot of time to complete the remaining work.
Now available on the prevalence of EDA tools software a lot, but in addition to the use of terminology and location of the function keys are different things are similar, and how to use these tools to better achieve the PCB design? before beginning the wiring on design for serious analysis and tools software carefully set will make the design more in line with the requirements. 　　The following is the General design process and steps. 1. determine the PCB layer circuit board size and wiring layer needs to be determined at the design stage. If the design requires the use of high-density ball grid array (BGA) components, you must consider these device wiring required a minimum of wiring layers. The number of wiring and cascading (stack-up) have a direct impact on the printed line wiring and impedance. 　　Plate size helps to determine the cascade and printing line width to achieve the desired design effects. Over the years, people always think circuit layers less costs lower, but the impact of the circuit board manufacturing costs and many other factors. In recent years, multilayer PCB cost differences between has been greatly reduced. When you start to design the best use of circuit-layer and make deposited copper uniform distribution, to avoid when designing the end found that a small amount of signal does not conform to the defined rules and space requirements, thereby forced to add a new layer. 　　In the design before careful planning will reduce wiring in a lot of trouble. 2, design rules and limit automatic routing tool itself does not know what to do about nothing. For the complete wiring, wiring tool needs the right rules and restrictions. Different signal lines have different routing requirements, special requirements on all the signal lines to categorize different design category. Each signal class should have priority, the higher the priority, the more strict rules. Rule involves printing line width, the maximum number of holes, parallelism, signal line, the interplay between the layers, which rules on wiring tools has a great impact on performance. 　　Carefully consider the design requirements were successfully route important step. 3, component layout for optimized Assembly procedure, design for manufacturability (DFM) rules will have on the component layout. If the Assembly sector allows components to move, you can optimize the circuit due to automatic wiring easier. 　　The definition of rules and constraints affecting the layout design. When the layout regardless of the routing path (routing channel) and through-hole area. 　　The path and the area on the designer, is obvious, but the automatic routing tool once will only consider a signal by setting a wiring constraints and set to Chief signal line layer, you can make the wiring tools like designers foreseen complete wiring. 　　4, fan-out design at the design stage, fan-out to enable automatic routing tool can connect to the component pins, surface-mount devices of each pin should have at least one hole for more connections, circuit board to the inner connection, in-circuit test (ICT) and the circuit and then processed. In order to enable the automatic routing tools the most efficient, be sure to use the largest through-hole size and printing lines, the interval is set to 50mil more desirable. To use the routing path few largest through-hole type. For fan out design, taking into account the in-circuit test. 　　Test fixtures can be very expensive and is usually invested in the upcoming full production is ordered, if the time to consider adding nodes to achieve 100% Testability is too late. After careful consideration and projections, in-circuit test design can be carried out in the design of the early, late in the production process, according to the routing path and in-circuit test to determine the type of fan out of the hole, the power supply and grounding also affects the wiring and fan-out design. 　　To reduce the filter capacitor connector resulting gankang, through-hole should be as close to the surface-mount devices pin, if necessary, manual wiring, it could have on the original vision of wiring paths, or even may cause you to reconsider what the through-hole and must therefore be considered the hole and PIN inductance between resistance and set the priority of the hole specifications. 5, manual, wiring and key signal processing although this article primarily discusses automatic wiring problems, but manual wiring in present and future are printed circuit board design is an important process. Manual routing help autorouting tools complete wiring work. 　　Figure 2a and 2b illustrates, through the selection of the network (net) for manual routing and be fixed, can be formed automatically when routing path can be based. Regardless of the number of key signal, first of all on these signals are wiring, cabling, or manually combined with automatic routing tool. Key signal usually must through careful design of the circuit to achieve the desired performance. Wiring is complete, then from the project staff to check the signal wiring, this process much easier.　　Check, if enacted, will these lines, and then start on the rest of the signal for autorouting. 6, autorouting on key signal wiring in some electrical wiring to control parameters, such as decreasing inductance and EMC, etc, for other signal wiring is similar. All EDA manufacturers will provide a way to control these parameters. 　　In understanding what the automatic routing tools, as well as the input parameter is an input parameter to the wiring, the automatic routing of quality, to a certain extent, can be guaranteed. Should adopt the General rules onSignal for autorouting. By setting restrictions and prohibition of wiring area to qualify the given signal layer and referred to a number of the hole, wiring tools can be thought of as an engineer design to automatic routing. 　　If the automatic routing tool used by the layer and the Chief of the hole number without restriction, automatic wiring will use to each layer, and will produce a lot of the hole. In the set of constraints and rules created by the application, the automatic routing will achieve the expected results of a similar, but of course you may also need to be some consolidation, but also the need to ensure that other signal and network cabling. 　　After the completion of the part design, fixed it, to protect against the effects of the process behind the wiring. Using the same steps for the remaining signal wiring. Routing number depends on the circuit of complexity and your definition of general rules. Every time you complete a signal, the rest of the network cabling constraints will be reduced. But followed many signal wiring requires manual intervention. Now automatic wiring tools are powerful and can usually be completed 100% of the wiring. 　　But when the automatic routing tool does not complete a full signal wiring is required on the remaining signal for manual routing. 7. automatic routing of design elements include: a slight change in settings, 7.1 try multiple path routing;
7.2 maintain basic rules, try different wiring layer, different printing line and interval width and different line widths and different types of through-hole such as blind and buried hole, observation of these factors on the results of the impact of the design;
7.3 let wiring tools on the default network are processed as required;
7.4 signal less important, automatic routing tools on its route, the greater the degree of freedom. 8, route finish if you are using EDA tools software is able to list the length of signal wiring, check these data, you may find some constraints are minimal length of signal wiring. This problem is easier to handle, by manually editing can shorten the length of signal wiring and reduce the number of the hole. In the finishing process, you need to determine which route is reasonable, what wiring unreasonable. 　　As with manual wiring design, automatic routing design can also be carried out during the check the collate and editing. 9, the appearance of the circuit board design often pay attention before the Visual effect of the circuit board, now is not the same. Automatic design of circuit boards than manual design of appearance, but in electronic characteristics to meet the requirements and design integrity cannot be guaranteed.

【School】 split air-conditioning repair weak detection】.

Split air conditioner both refrigeration system or electrical control system than the window type air conditioner is more complex and, therefore, in the analysis and check failure, should be careful and precise. One observation method

Use observation detection camion health, is the repair process to determine a common approach to malfunction. Example: start air conditioner refrigeration Compressor 3 minutes later, the outdoor unit external valve. Hydraulic tube condensation phenomenon appears, run 10 minutes later, the trachea, valve also appear frosting that air conditioner refrigeration operating normally, the refrigeration system with refrigerant.

To start the air conditioner refrigeration compressor, hydraulic valves, hydraulic pipe a began Frost, a few minutes later, cream and melted into the dew, and running in 15 minutes, trachea, dew valve appears, indicating that the air conditioner refrigeration system and a slightly less fluoride, but also basic enough, generally do not need additional refrigerant. To start the air conditioner refrigeration compressor, hydraulic valves, hydraulic pipe appear Frost, about 15 minutes after the trachea, valve also Frost, indicating that the refrigeration system is adequate, refrigerant is indoor units of air filters too dirty, hot swap effect is not good.

To start the air conditioner compressor is running, the start valve. liquid pipe appear Frost, Frost after several minutes, but not in the more-more than ten minutes, and run the pipe, valve has no dew or frost, indicating that the refrigeration system leakage of refrigerant has seriously, you need to conduct supplemental fluoride.

To start the air conditioner compressor running time, still no hydraulic valves, hydraulic pipe appear dew or frost, indicating that the refrigeration system with refrigerant leakage after all, the need for refrigeration system thoroughly serious leak after leak, exclude, and then restart filling refrigerant.

Second test method

Detection of camion is faulty, you can also use the test method to carry out its work in good health or judgement. Specific methods are: use a thermometer to test air conditioner indoor unit and export air temperature difference in air conditioners for cooling operation, when refrigeration compressor start running after 15 minutes, import and export air temperature difference to reach more than 80C (summer temperature in 350C following); winter heating time (outside ambient temperature above the 70C) compressor running in 15 minutes, import and export air temperature to achieve more than 140C, air conditioner refrigeration and heating effect is good. Use the clamp ammeter measuring air conditioner run-time operating current value, current value close to the rated current values, the air conditioner works fine, if measured operating current value is far greater than the rated current values, the air conditioner is bad, in overload status; if measured running current value is far lower than the rated current values on the compressor is in the light condition, the refrigerant in the refrigeration system are more serious leaks. Use gauges to test air conditioner refrigeration system working pressure, refrigeration of indoor units at runtime to run the table pressure at about 0.4MPa ~ 0.5MPa systemheat indoor unit running table pressure if around the 1.5MPa ~ 2.1MPa, are normal. If the pressure deviation from these two too many values, descriptions a/c is not working properly.

In addition, you can split air conditioner refrigeration runtime condensation water excretion, to roughly determine whether normal air conditioners work status. By: when the air conditioner in the strong cold gear running in 15 minutes from outlet pipe mouth if observed have condensation drops out, the air conditioner works correctly, otherwise shows air conditioner does not work correctly.

【 Weak current College 】 e-mail ticket system overview 】

System Overview:
In an era of high-speed development of information, tickets for the electronic management is strengthened scenic meetings management, improve the management efficiency of an important means. Traditional tickets easily forged, easy replication and favor release, a change in revenue orchards cause serious loss of tickets, it is difficult to form a visitor access Park computer statistics, management, and other ills. The electronic ticket management will greatly enhance the tourism law, standardized and overall management of information technology, and promote the industrial structure, helping to improve the investment environment, increasing openness to the outside.

Many occasions in life requires the use of a variety of ticket (such as various scenic railway, road, maritime industries pay ticket), the traditional booking and ticketing management are to hand jobs, resulting in some specific peak hours, the dramatic increase in ticket sales personnel's labor intensity, productivity, and managers can no longer be accurate statistics to scientific and rational arrangement ticket sales staff, the end result is the cause of customer complaints.

High efficiency, low cost is the barcode technology in ticketing management system application features, combined with its own area of the bar code of advanced technology and products, using bar code technology to realize various ticket creation and automation management, so that the user really cumbersome manual ticket's farewell, low efficiency.

This system uses advanced electronic barcode producer identification technology and computer ticketing information management with identity management modernization, integration, real-time information, security and reliability features of the accounting of tightness. The traditional manual ticket work electronically, while enabling the ticketing management work towards a comprehensive automation and standardization, able to fundamentally resolve the ticket queries, ticketing status of labor intensity, enhance the ticket management efficiency and quality of customer service.

Bar code:
The barcode is by far the most economical, practical for an automated identification technology. The barcode technology has the following advantages: A. input speed: compared with keyboard input, bar code entry is 5 times the keyboard input, and enables instant data input ".
B £ ® high reliability: keyboard input data error rate of three per cent, using optical character recognition technology error rate for one, and bit error rate of less than a millionth of a bar code technology.
C £ ® collection informative: use traditional one-dimensional bar code once to capture information on dozens of characters, and 2-dimensional barcode can carry thousands of characters, and have automatic error correction capability.
D £ ® flexible utility: barcode labeling as a recognized means alone or with the identification devices to form a system of automatic recognition, and other control devices connected to automation of management.

System basic structure:
Bar code ticket card;
Barcode reading card devices (barcode printer or laser platforms);
Bar code ticket channel three-roll gate management machine (with bar code scanners/turnstile \ control host);
Electronic ticket application management software JT8.0 (barcode version);
Booking tickets for the PC, PC, report to the printer.