Friday, May 20, 2011
Japan's production of semiconductor devices, from five to seven parts. Usually only the first five parts, each part of the symbolic significance of the following:
Part one: the number indicates the number of effective electrode device or type. 0-Optoelectronics (i.e. photosensitive) diode triode and combination of the above devices, 1-diodes, 2 three-pole or has two additional device pn junction, 3-has four effective electrode or with three other device pn junction, the ones ones and so on.
Part II: Japan Electronic Industry Association JEIA registered marks. S-indicates the Japan Electronic Industry Association JEIA registration of semiconductor devices.
Part III: letter devices use material polarity and type. A-PNP-high frequency, low frequency pipe, B-PNP-C-NPN-high frequency, low frequency pipe, D-NPN-F-P control very very controllable silicon, Silicon-controlled rectifier, G-N control H-N base unijunction transistor, J-P pfet, K-N pfet, M-TRIAC.
Part four: a number in the Japan electronic industry association registered with sequence number JEIA. Two more integer-start from the "11", expressed in the Japan electronic industry association registered with sequence number JEIA; different companies performance the same devices can use the same sequence number; the higher the number, the more recent products.
Part five: letter of the same type of improved product logo. A, B, C, D, E, F means that the device is the improvement of the original models.
Air conditioning cold preservation principles are, in the cold store refrigeration of storage to improve cold storage based on relative humidity of the environment, and to adjust the freezer in a specific gas composition in the maintenance of normal physiological activity of the fruit, the effective suppression of breathing, evaporation, hormones, microorganisms and enzymes, delaying their physiology and metabolism, delaying ripening aging process and preventing deterioration of corruption, and keep the food fresh longer. Gas refrigerator gas regulator is the oxygen concentration from 21 percent to 3 percent to 5 percent, i.e. keeping cold storage is on the basis of high-temperature refrigerator, plus a set of controlled atmosphere systems, use temperature and control of oxygen content in two aspects together to achieve inhibition of postharvest respiratory status.
Atmosphere refrigerator from the West, the 1980s into China is the world's most advanced cold storage of fruits and vegetables fresh. She passed control of cold storage in oxygen, carbon dioxide, ethylene, etc of the content of gas composition, complemented by measures such as temperature, make the cold storage of fruits and vegetables in a "constant gas thermostat" status, in terms of freshness period or from fresh quality can achieve better results, low temperature freezer freshness is a single incomparable manner. Advantages: 1, extended freezer storage time, longer than conventional freezer 1-2 times, making the unit more flexible master sell time for higher economic efficiency; 2, improving the cold preservation, preservation quality, nutrient losses small; 3, adapt wide range is diverse; 4, air conditioned cold storage and easy management, convenient compact size, reducing cargo losses; 5, reduce energy consumption; 6, air conditioned cold dishes can be finite, mixed storage unit of Qi different fruits and vegetables do not affect each other.
Power equipment failure there are many and varied, but most are associated with fever. From infrared diagnostic perspective, usually divided into external and internal failure. We all know, power system operation, the current import experience because the current effect produces resistance loss in power transmission of the entire circuit on the myriad of connectors, connector or contact. Ideally, the transmission circuit in various connectors, connector or contact contact resistance is lower than some of the resistance connected to the conductor, connection parts for wear fever no faster than the adjacent conductor of heat, but once some connectors, connector or contact caused by poor connection, increasing contact resistance, the site will have more resistance losses and higher temperature rise, resulting in overheating. This class is typically a external failures.
External fault characteristics: high temperature, easy-to-local infrared camera found, if not timely processing, deteriorating fast, easy form accident, causing the loss. External failure accounts for a greater proportion of fault.
The so-called high-voltage electrical equipment, internal failure, mainly refer to the enclosed in the solid insulation material and device shell internal electrical circuit failures and insulation deterioration caused by a variety of failures. Because such a failure in the electrical equipment, and therefore reflect internal device appearance of temperature rise is very small, usually only a few K. Detection of such failures to detect devices require a higher sensitivity.
Internal failure characteristics: the proportion of small, temperature fault, damage, and on the infrared detection equipment requirements.
According to the relevant unit offered long-term measured data and a large number of cases of comprehensive statistics, external heat power equipment accounted for equipment defect defect general overall average of 90% ~ 93%, internal heat defect only7% to 10%.
In the electric power industry, very early on the thermal imager for device security overhaul, through its electrical equipment and wiring for detection of defects, such as transformers, bushings, circuit breaker, switch, transformer, electrical capacitors, lightning, power cable, straps, cables, switchgear, low-voltage electrical insulator strings, as well as current, voltage caused by heat or other thermal effect of equipment of secondary circuit, this timely detection, treatment, prevention of major accidents can play a very crucial and effective role.
The so-called thermal electric devices, commonly referred to by some means of detection, because of its intrinsic or extrinsic reasons caused by the phenomenon of fever.
According to the causes of defects, we are usually categorized into 3 types: one is the long-term exposure to air, due to the influence of temperature and humidity, or surface dirt and bad, or due to external effects arising from the injury, making part of conductive cross-sectional area to reduce the fever. If the connector, bolts, washers not pressed; long running corrosion oxidation; the atmosphere of active gas, dust, corrosion; components caused by bad installation materials, processing technology is not good cause conductor damage; mechanical vibration and other causes of conductor actual section lower; load current instability or exceeded.
The other type is due to electrical failure, such as inner itself internally connected parts is bad cause excessive resistance; insulating materials aging, cracking, peeling; internal component gets wet, pieces loss increment; cooling medium pipeline block, and so on.
For those who can directly observed equipment and pieces, infrared camera will be able to find all the connection points of vulnerability. For those who were unable to due to be screened directly see section, you can pass under its heat to the outside parts of the analysed thus concluded. Due to the ever-changing field of reality, even if you pass the thermal imager is a piece of a hot picture, if you want to make an accurate judgement, may be affected by many factors. As the current temperature, air flow, load, and so on. We can according to different characteristics, as related to analysis, to determine if:
In order to guarantee secure and efficient operation of electricity production, electricity equipment state maintenance set higher requirements. As a condition-based maintenance depends on the State of a running device detection and online monitoring tools, electric power equipment running status detection and monitoring the production of the electrical safety has always played an important role. Infrared imaging technology as a new technology, electric power equipment running detection has incomparable advantages. Infrared imaging is a device of the hot state distribution on devices running good or not for diagnosis, it has not stopped, non contact, distance, speed, visually on the equipment of hot for Imaging. Because device of thermography is a device running hot and temperature distribution in a true depiction, and power equipment in operation of heat distribution is normal or not in good enough condition to determine the device or one of the important characteristics, thus. Using infrared imaging technology can device thermography of analysis to diagnose the status of the device and its hidden defects.
Using infrared imaging technology to carry out the following electrical equipment condition monitoring and fault diagnosis.
● High-voltage electrical equipment operating status detection and internal and external Center Troubleshooting:
● Various conductive connectors, connector, wiring, corrosion and oxidation of pile head connected defects;
• Various types of high-voltage switches Center contact bad defects;
• Isolated knife, knife and touch tablet, as well as rotating CAP and ball head with undesirable defects;
● Various CT once outside the Centre in the Centre and connected defects, ontology and oil insulation defects as well as within the Center core, coil exception bad heat sink;
● Various PT insulation bad defects, lack of oil, as well as within the Center core, coil exception bad overheating faults;
● Various capacitors overheating, coupling capacitor oil insulation bad and the lack of oil (low oil level) defect;
● Various shortcomings in the center of moisture surge arresters, Center component aging or defects caused by nonlinear characteristics;
● Various insulators surface defects, polluted insulators detection, detection of vases; deteriorating
● The generator running detection, brushes and rings for contact status detection, overheating detection in the Centre;
● Power transformer box abnormal overheating overheating, Eddy current, high and low pressure casing on both ends of the connection, as well as the poor lack of oil oil casing (low oil level) defects；
• All types of motor bearing bad, and the in vivo Center abnormal overheating
Maintenance personnel often encounter no drawings of electronic products, according to the real draw circuit schematics. This is the beginner must master the basic skills, the following describes the methods and techniques.
1. Select the volume, PIN number and play a major role in the circuit of components such as IC, transformer, transistor and other painting map Datum element, and then select the baseline start for the PIN, you can reduce the error paint.
2. If the printed circuit board is marked with a symbol number (such as VD870, R330, C466, etc.), as these numbers have specific rules, after the first letters of the Arabic numerals of the same components within the same functional unit, so the paint should be specially with use. Distinguish the same functional unit of components, is the basis for drawing the layout.
3. If the PCB on the ordinal number of the components, for ease of analysis and correction circuit, the best one gives the number of components. Manufacturing plant in the design of PCB arrange components so that the shortest foil alignment, generally the same functional units of the relative concentration of components. Find a unit play a central role in the device, as long as this allows you to find the same functional units of other components.
4. distinguish PCB's ground, power and signal cables. To the power circuit, for example, power transformer secondary received negative side of the rectifier tubes for power cathode, and Earth are attached between General bulk filter capacitor, the capacitor shell have polarity signs. May also be obtained from the three-Terminal regulators pins to find out the power and ground wire. Factory in PCB wiring, in order to prevent the self-excited, anti-interference, general ground wire copper foil set most wide (high-frequency circuits are often large grounding copper foil), power cables copper foil, copper foil most narrow signal lines. In addition, in both analog and digital circuits of electronic products, PCB often separated from their respective ground to form independent grounding network, this can also be used as the basis for recognition of judgments.
5. in order to avoid too many components pin wiring makes the circuit wiring cross interspersed, resulting in the art of illustration messy, power and ground can make heavy use of terminal symbols the callout and grounding. If the components are more, you can also separate the unit circuit, painted and then grouped together.
6. sketch, recommend using transparent tracing paper, multiple color pen will ground wire, power cable, signal cable, components such as draw by color classification. Modify, gradually deepening colors, making the drawing intuitive smart so that analysis of the circuit.
7. be familiar with some basic cell circuit and composed form, such as the classic drawing rectifier bridge, voltage circuit and amplifier, digital integrated circuit, etc. First direct the cell circuit, circuit diagrams drawn framework that would improve the efficiency of the paint.
8. draw a circuit diagram, should as much as possible to find a similar product of circuit diagrams for reference, will play a more effective role.
Saturday, May 7, 2011
<br> along with projection technology continues to mature, in the hands of users Projector "figure" is mainly LCD projectors and digital projectors. .However, the use of such projector, projection color cast often encounter the problem, leading to a decline in projection. .So why do failures occur Projector color cast, when we encounter such a failure, how quickly to respond? Believe that the contents of this article below will give you a satisfactory answer! <BR> Color cast because normal projection ., the LCD projector's optical processing system through an internal, light will "break" into the red, green and blue color light beam, respectively, the three colors of light beam through the transmission, AD conversion, modulation and other processes, appears in three .LCD panel, and then through the optical path control unit, to achieve the proper color of light off the last three color light beams for projection prism synthesis, the formation of color image output through the projector lens on the projector screen. .The DLP projector is a digital-based red, green, and blue color wheel technology to the color of the image processing projection, the projection of the real extent of the color projector is closely related to the number of the DMD micromirror. .If the deal through the projector optical system, the output of the past. .Three-color projection light in a certain one or a few colors, then the image appears on the screen will appear obvious color cast problems. .Obviously the main reason for color cast caused by the projector, the projector is the internal optical processing system, by "external" interference, you can not correct the image color processing and "expression", but of course there's "external force" includes a number of factors ., caused by different factors need to use a different color cast projection methods to solve. .Color cast of the actual projection units have a Hitachi projector, the "service" time for nearly a half almost two years. .Most recently, do not know why, through the projector screen projector images out of total sensory phenomenon obvious color cast. .At first I thought it was Ougan cold, and do not mind this phenomenon, but in the days after the projection, projection color cast failure can never be eliminated, it is clear projector is really ill,. .In desperation, I decided to conduct some thorough examination of the projector. .I first connected the projector and computer lines were checked and found that the computer connected to the projector is the Founder of a Celeron 733 desktop, will not be connected to the projector's VGA cable and the computer took place within the mixed .line, leading to a serious projection signal crosstalk phenomenon? first anyway, or the first two VGA interface to remove the data cable to see! So I for a penny, in for a pound, quickly recruited multimeter, open the VGA cable .both sides of the interface, and each of them were detected signal lines, the results did not find the signal wire hinge, such as break and short circuit fault. .In order to verify the projector or the signal line is faulty, I also used a data cable with a VGA projector and another computer connected, powered on again, and found that the output of the projector on the projection screen in the curtain has not .color cast phenomenon occurs, and the results look very clear, very clear and Flanagan VGA projector cable is normal, the problem is most likely connected to the projector that sets Founder previously caused the computer. .So that sets the author of the Founder computers were examined, to see the computer's display resolution parameters, whether within the support of the projector; When I open the Display Properties settings Founder Computer window, find the computer's "color" .parameter is set to 16 colors enhance the color, "Display Resolution" parameter is set to "800x600", "Refresh resolution" parameter is set to 75Hz; each of these parameters associated with the technical specifications of the projector comparison, the .Founder of the computer that the projector supports all display parameters, indicating that the fault is not a projection color cast caused by the Founder of the computer itself! through some of these efforts to come to the preliminary analysis of the results: VGA cable and the projector itself is normal .connecting the projector Founder PC is normal, projection display parameter settings are correct. .Then in addition to the above factors may cause the projector malfunction, what factors can lead to projector failure occurred color cast it? Will not be connected with the projector power cable caused the power outlet it? I think to do, pull up .all the plugs out of the socket and power outlet with a multimeter on the output voltage detection, but test out the value that the electrical outlet power supply stability, there is no unusual places. .But I do not trust the results of the test, intended to use to buy a new outlet to replace what, after all, can be confirmed through the substitution is really a faulty electrical outlet, so you can narrow the scope of troubleshooting, improve troubleshooting efficiency. .When I bought it with the new replace the old socket outlet after a miracle indeed, the original failure occurred Projector color cast, and now the projection is very clear and it did not have any color cast phenomenon. .Why is it so!? I fail to understand why, do little power outlet can also be set off so much of the "storm"? Outlet through some of the old "open gut belly breaking", the author found that the zero line of the internal socket .turned out to be "crimes Huai culprit." .Ground within the original socket and the zero line accidentally touched together, in the absence of the plug connection with a multimeter to test the power outlet, it will show the tests are normal, but once plugged in, then, between the zero line and the line of fire .The power supply circuit, will result in ground socket will be charged, a result in line current will return through the plug to the projector and computer projector so easily lead to the interference signal by the signal, resulting in projection .color cast problems. .When I try to plug the internal ground and separated from the zero line, while ensuring a reliable power outlet grounded again after the projector and computer connected to the fixed projection on the old socket, the projection color cast failure turned immediately disappeared. .Projector color cast caused by the projector response occurred in fact, there are many factors color cast, caused by different factors projection color cast failure, need to use different methods to deal with. .To help you projector users to effectively and quickly eliminate color cast fails, the author summarizes some of the following deal specifically, and I hope you can bring help! 1, we know that timely replacement of projector bulbs, projector bulbs each have a certain .life, close to the lamp life projection that time, the bulbs are often unable to deal with the projector out of the image color fidelity, clearly revealed itself, a dim image of a color picture often gives people the feeling of color cast .. .To remove the light bulb does not light color cast caused by failure, the only way is the timely replacement of projector bulbs, projection color to highlight again, clearly is output to the projector screen. .It should be noted that the projector lamp is best to use and consistent brand, and install the bulb, do not touch the bulb directly, because light bulbs have a special protective surface layer, if the direct hand contact, may be .leave marks on its surface, thus affecting the projection color output. .2, the signal line is connected correctly Many people think that the signal line connecting the projector is a very easy thing, but the more simple things, the more often the introduction of neglect. .This does not, once the projector signal cable is not securely fixed to the computer or the projector's VGA port, it may be bad phenomenon, this phenomenon of projection color cast failure is often difficult to be noticed. .In addition, the signal line interface to a computer or projector into the VGA port, if the location of the closed, plug too much force, it is easy to interface the signal cable core needle bend or break, which would also easily lead to .Projector color cast failure occurred. .There are connecting the projector and computer VGA signal cable length of more than 15 meters, then the projector will be seriously degraded signal, which would inevitably arise projection color cast problems. .In order to eliminate the signal cable failure caused by improper projector color cast, you must do the following: First, the signal cable connected to the VGA port, the first aimed at the port location, and then the appropriate force to ensure the signal line interface .VGA port needle core and reliable access, do not use brute force in the insertion, broken needle core; then the trouble to carry forward the spirit, tighten the screws for the fixed position to ensure that the projector with the VGA port signal line between the stable .are firmly connected together, can not have the slightest shaking; in the selection of the data projector line, please try to use the complimentary projection signal line, and not free to use other projectors to replace the signal line; another signal to prevent the projection .excessive attenuation, make sure the cable length can not use more than 15 meters; <BR> Once a phenomenon projection color cast, try to use the signal cable directly to the projector connected to the computer instead of using the display or signal amplifier distributor .because the color cast failure may also be handled by the link between these signals caused. .3, in the long time maintenance of your hand during use, some components inside the projector often occur aging, or internal components often move the projector, there will be loose, shedding phenomenon, this can lead to projector .Projector color cast failure occurred. .Under normal circumstances, the projector to solve the poor due to their own hardware failure caused by the projection of color cast, the better if a professional repair service personnel to detect, rather than yourself, free to open the projector housing, it is easy to damage the projector off .machine. .4, projection parameters set the color if the projector displays the computer screen parameters and parameters are not consistent, or if the color inside the projector display parameters not set correctly, then the projector may also lead to occurrence of color cast problems. .In the elimination of failure in this regard, as long as the patient and meticulous, will re-adjust the projection parameters are for; In addition, as much as possible to the projector and computer to adjust the display parameters appropriate to ensure that they accurately match. .5, away from the electromagnetic signal interference as the projector signal cable to transmit the signal, such signals are susceptible to external electric or magnetic field interference, which occurs projection screen color cast caused by failure or instability. .To avoid such a failure occurs, you should not be the projector signal cable and power lines or other communication cables close together and do not let the signal cable through the doors, windows crack, not in a strong magnetic signal .where the projection shows <BR>.
How to identify common components?
Resistor in a circuit using the "R" with figures, such as: R1 indicates that the number 1 of resistance. Resistor in a circuit's main role is: triage, current limiting, divider, bias, and so on.
1, parameter identification: units for Ohm resistance (Ω), multiplying the unit: thousand euro (K Ω), megohm (M Ω), etc. Conversion
By: 1 megohm = 1000 thousand euro = 1000000 Europe
Resistance of parameter annotation methods are 3, i.e. direct standard method, color standard method and a few standard method.
A number of standard method, mainly for the patch and other small volume of the circuit, such as: 472 represents 47 × 100 Ω (i.e. 4.7K); 104 indicates 100K
B, color ring marking method most used are for example: four color ring resistance multicolored resistors (precision resistors)
2, resistance of color stops location and rate relationships as shown in the table below:
Color number times the rate of the allowed deviation (%) silver/x0.01 ± 10 Golden/x0.1 ± 5 black 0 + 0/Brown 1x10 ± 1 red 2x100 ± 2 Orange 3x1000/yellow/green 4x10000 5x100000 ± 0.5 blue 6x1000000 ± 0.2 grey purple 7x10000000 ± 0.1 8x100000000/white 9x1000000000/
1, capacitance in the circuit of general use "C" with a number (such as C13 represents number is 13 capacitance). Capacitor consists of two pieces of metal film immediately, separated by the insulating material is separated from the composition of elements. Capacitance characteristics mainly at DC-AC.
The size of the capacitor capacity is expressed to the size of the storage of electrical energy, capacitance on AC signal impediment is known as the capacitance, and AC signal frequency and power capacity.
Capacitance XC = 1/2 to π f c (f represents the AC signal frequency, the c = capacity) telephones are commonly used in a variety of capacitance electrolytic capacitors, ceramic capacitors, chip capacitors, monolithic capacitors, tantalumcapacitor and polyester capacitors, etc.
2. identification: identification of capacitance and resistance of recognition method is basically the same, divided into direct standard method, color standard method and a few standard method 3. The basic unit of capacitance for farad (F) that the other units also: MW (mF), micro (uF), NA (nF), skin (pF). Of which: 1 Farah = 103-method = 106-method = 109 na method = 1012 skin method
Capacity of the capacitor capacity values marked directly on the capacitor, 10uF/16V
Capacity of small capacitor capacitance values in its capacity on the letter or number
Letter notation: 1m = 1000uF1P2 = 1.2PF1n = 1000PF
Digital presentation: generally uses a three-digit number represents the size, the first two digits represent a valid number, first 3 digits is multiplying.
Such as: 102 represents 10 × 102PF = 1000PF224 represents 22 × 104PF = 0.22uF
3. capacitance tolerance table
Allowable error of ± 1% ± 2% ± 5% ± 10% ± 15% ± 20% if: a porcelain capacitor-104J represents a capacity 0.1uF, a tolerance of ± 5%.
3. Crystal diode
Crystal diode in circuit common "D" with a number, such as: D5 represents number 5 of the diode.
1, role: main character is a diode in one-way conductivity, which is in the forward voltage, on-resistance is very small; in reverse voltage of on-resistance of great or infinity. Because of these characteristics, a diode with a cordless phone in it is used in commutation, isolation, voltage and polarity protection, coding control, FM modulation and static noise and other circuits. Telephones in use of Crystal diode by role can be divided into: rectifier diode (such as 1N4004), isolation diode (such as 1N4148), Schottky diodes (such as BAT85), light emitting diodes, Zener diodes, etc.
2. identification: identification of the diode is very simple, small power diodes n pole (anode), most of the diode appearance using a color circle marked out, some diodes with dedicatedsymbols to represent diode P pole (cathode) or n pole (anode), also have a symbolic sign for the "P" and "N" to determine the diode polarity. Light-emitting diode polarity can be identified from PIN length, long foot is positive, negative short legs.
3. test considerations: use digital multimeters to measure diode, diode red table pen, black table of cathode diode anode of the pen, the measured resistance is the diode is Wizard-resistance, this pointer table pen connected multimeter method is exactly the opposite.
4, commonly used 1N4000 series diode voltage comparisons are as follows:
Withstand voltage (V) 501002004006008001000
Current (A) are all 1
Fourth, the Zener diode
Zener diode in circuit common "ZD" plus digital representation, such as: ZD5 represents number 5 voltage tube.
1 Zener diode voltage principle: Zener diode is characterized by the breakdown of both ends of the voltage has remained virtually unchanged. Then, when the regulator hose access circuit, if due to the power supply voltage fluctuations, or other causes circuit voltage changes in various points, load both sides voltage will remain unchanged.
2, fault characteristics: Zener diode breakdown mainly in open circuit, short circuit and voltage values are not stable. In these three failures, previous failures shows the power supply voltage to rise; after 2 failure performance for the power supply voltage to low to zero volts or output stability.
The model of the common Zener diode and voltage values are as follows:
Voltage value 3.3V3.6V3.9V4.7V5.1V5.6V6.2V15V27V30V75V
Inductor in circuit common "L" with figures, such as: L6 represents number 6 of the inductance. Inductance coil is insulated wire skeleton in insulation around a certain number of turns. DC to DC resistance through the coil, it is the resistance of thewire itself, pressure drop is very small; when the AC signal through the coil, coil ends will produce from EMF EMF, since the direction of the applied voltage in the opposite direction, obstacles to communicate through, inductance characteristics is pass DC resistance, the higher the frequency, the greater the impedance of the coil. Inductance in the circuit can be composed of the oscillation circuit capacitance. Inductance General direct standard method and color stop method, the stop method is similar to the resistance. Such as: Brown, black, gold, gold said 1uH (error 5%) of the inductance. The basic unit of inductance: Heng (H) conversion units are: 1H = 103mH = 106uH.
6. variable capacitance diode
Varactor diodes are based on normal diode internal "pn" junction capacitance can vary plus reverse voltage changes this principle specially designed a special diode. Varactor diodes in the cordless telephone is mainly used in mobile or fixed-frequency modulation circuit, the realization of low-frequency signal modulated to high-frequency signals, and fired away. In working order, normal voltage variable capacitance diode modulation to the anode, the internal junction capacitance diode capacitance with the modulation voltage changes.
Variable capacitance diode failure, mainly for leakage or performance variation:
(1) occurs leakage phenomenon, high-frequency modulation circuit will not work or a performance variation.
(2) the evolution of performance variation, high-frequency modulation circuits of precarity, the modulation of high-frequency signal is sent to the other side is received after distortion.
One of the above situation occurs, you should replace the same model of varactor diodes.
I. RS-232, the origin of RS-422 and RS-485
RS-232, RS-422 and RS-485 are serial data interface standard, initially by the electronic industries Association (EIA) developed and published, the publication in 1962 RS-232, named EIA-232-E, as industry standards, to ensure that the different manufacturers are compatible between products. RS-422 evolved by RS-232, it is not enough to compensate for the RS-232. To improve short-232 communicate distance, rate, low defect RS-422 defines a balanced communication interface, transfer rate up to 10Mb/s, transmission distance extension to 4000 feet (rate is lower than 100kb/s), and allow a balance between the bus connection up to 10 receivers. RS-422 is a stand-alone sent, many computer receives one-way, balance transfer specification, being named the TIA/EIA-422-A standards. To extend the application range, EIA and in 1983 has developed on the basis of RS-422 RS-485 standards, increased the number of points, bidirectional communication capability, which allows more than one transmitter is connected to the same bus, at the same time increased transmitter drive capability and conflict protection characteristics, common-mode range expanded bus, named after TIA/EIA-485-A standards. Because standard EIA recommendations are prefixed by the "RS", so in the communications industry, still accustomed to the standard RS for prefix titles.
RS-232, RS-422 and standard only on interface RS-485 electrical characteristics, without involving the connectors, cables, or Protocol, users can create their own high level communication protocol. Therefore the application of the video border, many manufacturers have established a set of high-level communication protocol, or open or exclusive use of manufacturers. If the video recorder manufacturers of Sony and Panasonic on recorder RS-422 control protocol there is a difference, video server control protocol is more, such as the Louth, Odetis Protocol is open to the public, and ProLINK is basedon the Profile.
2. RS-232 serial interface standards
Currently RS-232 is between PC and communication industry's most widely used a serial interface. RS-232 is defined as a low-speed serial communications increase the communication distance of single standard. RS-232 take unbalanced transmission mode, the so-called single communication.
The beginning of the data collected, the signal is relative to the signal, e.g. from DTE device data when using the DB25 connector is 2 feet relative 7 feet (signal) level, the PIN DB25 defined see Figure 1. Typical RS-232 signals in positive and negative voltage swing, in between sending data, send-side drive output is terminated at + 5 ~ + 15V,-in-5 ~-15V-level. When no data transfer line for TTL, transfer data from start to end, line-level from the TTL level to the level of return RS-232 TTL level. Receiver typical working level in + 3 to + 12V-12V-3 ~-. Because the send level and receive the level of difference of only about 2V to 3V, their common-mode rejection differential, and twisted-pair on distributed capacitance, its transmission distance up to about 15 meters, the highest rate for 20kb/s. RS-232 is for peer to peer (that is, only one pair, receive device) communication, its drive load is 3 ~ 7 k Ω. So RS-232 suitable for communication between the local device. The electrical parameters see table 1.
III. RS-422 and RS-485 serial interface standards
1. balance transfers
RS-422, RS-485 and RS-232, data signal using differential transmission mode, also known as balance transfers, it uses one pair, is one of A line is defined as a line is defined as B, as in Figure 2.
Typically, send drive A, B are level in between + 2 to + 6V, is a logical status, negative-in-2 ~ 6V, is another logical state. Another signal to C, there are a "RS-485 enabled" side, but it is available in RS-422 may be unused. "Enable" is used to control the sending off of the drive and transmission lines and connections. When"enabled" end-to-work, sending the drive is in high-impedance state, known as the "third State", i.e. it is different from a logical "1" and "0" in the third State.
The receiver also made and sending end relative to the beginning of the collection, will be through balanced twisted pair AA and BB corresponding connected, when in the end there is greater than + AB 200mV power, output is logic level that is less than-200mV, output negative logic level. Sinks receive balanced line level range is typically between 200mV to 6V. See Figure 3.
2.RS-422 electrical requirements
The full name is "RS-422 standard balanced voltage digital interface circuit of the electrical characteristics", which defines the characteristics of the interface circuit. Figure 5 is a typical RS-422 four-wire interface. In fact there is also a signal ground, all 5 lines. Figure 4 is the DB9 connector pin definitions. Because the receiver uses the high input impedance and send drives than RS232 stronger drive capability, it allows the same transmission line to connect multiple receiving node, maximum 10 node. That is a primary (Master), the rest is from devices (Salve) from device cannot communicate, so support point-to-many RS-422 two-way communications. Receiver input impedance is 4 k, so the beginning of the maximum load capacity is 10 × 4k + 100 Ω (terminating resistor). RS-422 four line interface as a separate transmit and receive channel, so you don't have to control the data direction, each appliance must be between any exchange of signals can be set by software (XON/XOFF handshaking) or hardware (a separate twisted pair).
Most RS-422Large transmission distance to 4000 feet (1219 m) with a maximum transfer rate is 10 MB/s. Its balanced twisted pair to the length of the inversely with the transfer rate, in 100kb/s rate following, will it be possible to achieve the maximum transmission distance. Only a short distance down to get the highest transmission. Typically 100-metre-long twisted pair on the maximum transfer rate is only 1 MB/s.
RS-422 need a terminating resistor, request its resistance is about transmission characteristic impedance of the cable. At the moment distances can be without terminating resistor, which is usually in the 300 m without terminating resistors. Terminating resistor connected to the most remote transmission cable.
RS-422 for electrical parameters are shown in table 1
3.RS-485 electrical requirements
Because RS-485 is developed on the basis of from RS-422, so with many electrical RS-485 RS-422 similar. If using balanced transmission mode, all need in transmission line connecting terminating resistor, etc. RS-485 can take second-line and 4-wire, 2-wire system can achieve true multipoint two-way communication, see Figure 6.
A four-wire connection, and the like can only achieve RS-422 point-to-many communications, which can only have one primary (Master) device, the rest is from the device, but it has improved, both RS-422 four-line or second-line connection bus can be received 32 devices. Refer to Figure 7.
RS-485 and different RS-422 lies in its common-mode output voltage is different, RS-485 is-7V to + 12V,-7V RS-422 to + 7V, RS-485 sink minimum input impedance 12k sword bao Jian S-422 is 4k; old a chance Istmo shoot movement S-485 meet all specifications, so RS-422 RS-485 drive can be used in the network application in RS-422.
The provisions relating to the electrical RS-485 see table 1.
RS-485 and RS-422, its maximum transmission distance of about 1219 meters, the maximum transfer rate is 10 MB/s. Balanced twisted pair to the length of the inversely with the transfer rate, in 100kb/s rate following provisions can only be used a maximum cable length. Only a short distance down to get the highest transmission. Usually 100 metres long twisted pair maximum transfer rate is only 1 MB/s.
RS-485 need 2 terminating resistor, its resistance requirements equivalent to transfer characteristicimpedance of the cable. At the moment distances can be without terminating resistor, which is usually in the 300 m without terminating resistors. Terminating resistor connected to the ends of transfer bus.
IV. RS-422 and RS-485 network installation points
RS-422 can support 10 nodes, RS-485 support 32 nodes, so more nodes on the network. Network topologies generally use terminal bus structure that matches does not support ring or star network. In building the network, you should be aware of the following:
1. using a twisted pair cable for bus, the individual nodes concatenated together, from the bus to each node of the PIN length should be short, so that the PIN in the reflected signals influence on bus signals. Figure 8 illustrates the practical application of the common mistakes connection methods (a, c, e) and the correct connection methods (b, d, f). A, c, e three network connection although it is not correct, in short, low rate might still be working, but as the communication distance of extended or communication rate increases, its adverse effects will be more and more serious, mainly because of the signal in the end of each branch and the original signal reflected, the overlay will cause signal loss of quality.
2. it should be noted that bus the characteristic impedance of continuity, the resistance is not continuous point occurs signal reflection. The following easy to produce such discontinuities: bus different sections with different cable, or a section of the bus there are too many transceivers are right next to each installation, moreover is overly long branch line leads to the bus.
In short, should provide a single, continuous signal path as the bus.
V. RS-422 and RS-485 transmission lines that match some instructions on the
On RS-422 and RS-485 bus network typically uses to match a terminating resistor. But a short distance and low rate can not consider terminator. So in what circumstances do not consider matching? theoretically, in every receiving data signal sampling point, as long as the echo signal attenuation at the start of sampling is to low enough to not consider matching. But this in fact difficult to grasp, United States MAXIM company article mentioned an empirical principles can be used to determine what data rate and the length of the cable match when needed: when signal conversion time (increase or decrease) over electrical signals along the bus one-way transmission time 3 times above can not match. For example with finite slope of 485 MAX483 output signal rise or fall time 250ns minimum, typical twisted pair signal transmission rate on about 0.2m/ns (24AWGPVC cable), then as long as the data rate in 250kb/s or less, cable length not more than 16 meters, using MAX483 as RS-485 interface can not match with the Terminal.
General Terminal matching terminating resistor method used, the previously mentioned already, the RS-422 in bus cable and distal resistor RS-485 then bus cable's start and end are required and then terminating resistors. Terminating resistors generally remove RS-422 network 100 Ω, RS-485 network took 120 Ω. Equivalent to the cable impedance of resistance, since most twisted-pair cable characteristic impedance is approximately 100 ~ 120 Ω. The match method is simple and effective, but there is one disadvantage, matching resistor to consume less power, power consumption limit comparison strict system does not quite fit.
Another comparison saving match is a match, RC in Figure 9. Use a capacitor C partition DC components can save most of the power. But the capacitor C's takeValues is a difficult, you need to match the power and quality tradeoff between.
There is a diode matching method, as in Figure 10. This scenario was not true of the "match", but it uses the role of the clamp diode can quickly undermine the reflected signals, to achieve the aim of improving the quality of the signal. Significant energy saving effects.
6. RS-422 and grounding problems RS-485
Electronic system grounding is important but often overlooked. Improper grounding treatment often leads to electronic systems are not stable work even endanger the system security. RS-422 and RS-485 transmission network of ground is also a very important, because the ground system is not reasonably affect the stability of the entire network, especially in the working environment more harsh and transmission distance, the requirements for the grounding. Otherwise interface with high failure rate. In many cases, connecting RS-422, RS-485 communication link is simply a pair each interface of the "A" and "B" end. Ignoring the signals of connection that this connection method in many occasions is working properly, but they have great trouble, which has the following two reasons:
1. common mode interference problems: as previously stated, RS-422 and RS-485 interface uses the differential for the transmission signal and does not need to be relative to a reference point to detect the signal, the system only needs to detect the difference between the two lines. But people tend to ignore the transceivers have certain common-mode voltage range, such as RS-422 common-mode voltage range is-7 to + 7V, RS-485 transceiver common-mode voltage range is from-7 to + 12V, only meet the above conditions, the entire network to work correctly. When the network cabling common mode voltage outside this range will affect communications for the stable and reliable, even damage the connector. In Figure 11, for example, when you send a drive A to B to send data to the receiver, and send the output of the drive a common-mode voltage for VOS, because the two systems have separate earthing system, there is a real potential difference VGPD. Then the receiver input common-mode voltage VCM will achieve VCM = VOS + VGPD. RS-422 and standards require RS-485 VOS ≤ 3V, but VGPD probably a significant (more than 10 volts or even dozens of volts), and may be accompanied by strong interference signal, the receiver CMR VCM beyond the normal range, and transmission line interference current, light is impacting communication, then the damage communications interface circuit.
2. (EMI) issues: send drive output signal of the common parts require a return path, in the absence of a low resistance of return channel (signal), it will return a radiation source, the entire bus and it seems like a giant antenna to radiation of electromagnetic waves.
For these reasons, although adopting RS-485 RS-422, differential balanced transmission mode, but on the whole RS-422 or RS-485 network, you must have a low resistance to the signal. A low resistance signal to two interfaces are connected with the work, so that the common mode interference voltage VGPD is short. This signal can be an additional line (unshielded twisted pair) or STP shielding layer. This is the most common grounding method.
It is worth noting that this approach only on high-effective, common mode interference due to the interference source resistance, short answer would not be formed very large ground loop current, the communication does not have a significant impact. When the common mode interference resistance is low, will be grounded on a large loop current, affect the normal traffic. In my view, you can take the following three measures:
(1) if the source of interference is not inner resistance is very small, you can add current limiting resistor Earth wire to limit the interference currents. Grounding resistance increase might cause the common-mode voltage rise, but as long as the control in the appropriate context will not affect the normal traffic.
(2) use of floating ground technology, cut off ground loops. This is more commonly used is also very effective in such a way that when the common mode interference resistance is small the above method does not work, you can consider the introduction of interference of the node (for example in a poor working environment of on-site equipment) floating up (that is the system of the circuit with the enclosure or earth isolation), partition a ground loop, will not form a large loop current.
(3) use of isolated interface. In some cases, for security or other concerns to the circuit must be connected to the enclosure or the Earth cannot be suspended, and you can isolate the interfaces to cut off ground loop, but still should have a ground wire will isolate the public side of the side and the other interface to work. See Figure 12.
VII. RS-422 and network failure protection RS-485
RS-422 and RS-485 standards provide the receiver threshold ± 200mV. Such requirements can provide higher noise suppression capability, as mentioned, when the receiver A level higher than the level B + 200mV above, the output is logical, on the other hand, the output is negative logic. But because of the existence of a third State, that is, the host in the beginning of the end of the message data, the bus on the third State, that is, the bus is idle with no signal bus, so that the voltage between AB-200 to + 200mV until tends to 0V, this poses a problem: the receiver output status is not OK. If the receiver output to 0V, network from the machine will be interpreted as a new start bit and tried to read subsequent bytes, as never have the stop bit, produce a frame error as a result, there is no longer a device requests a bus network to a standstill. In addition to the above mentioned bus idle will cause two line voltage difference below 200mV, open circuit or short circuit when they happen. It should take certain measures to avoid the receiver is in an indeterminate state.
Usually on the bus on the bias, when bus free or open-circuit, use bias resistor will bus bias in a certain State (differential voltage ≥-200mV). As in Figure 13. Will A pull-up to, B drop-down to 5V, the resistance of a typical value is 1 k Ω, specific capacitance values over cable.
The above methods is a more classical approach, but it still does not solve the problems of short bus, some manufacturers will receive threshold to-200mV/-50mV, can solve this problem. For example, Maxim company MAX3080 series RS-485 interface, not only eliminates the external bias resistors, and resolved the bus short-circuit failure protection issues.
VIII. RS-422 and transient protection RS-485
Previously mentioned signal grounding measures, only the low frequency common mode interference has a protective effect, for the high frequency interference is incapable of transient. As a result of the transmission line in relation to the high-frequency signal is the equivalent of inductance, so for high-frequency interference, grounding line transient actually equivalent to pave the way. This transient disturbances while the duration is short, but there can be hundreds or thousands of volts.
The actual application environment or the existence of high-frequency interference may be transient. General switching power inductive load such as motors, transformers, relays, etc. or lightning process generates amplitude high transient interference, if not properly protection will damage RS-422 or RS-485 communication interface. For this transient disturbances can be quarantined or bypass of protection.
1. isolation protection method. This program will actually be transient-voltage transfer to isolate interface in electrical isolation layer, because of the isolation layer high insulation resistance, will not produce damaging surge current, played the role of protection interface. Usually uses the high frequency transformers, optical coupling, and other components implement electrical isolation, device manufacturers will all these components are integrated in a chip IC, using very simple, such as Maxim company MAX1480/MAX1490, isolation voltage can be up to 2500V. This solution has the advantage that can withstand high voltage, duration longer transient disturbances, and more easily implemented, the disadvantage is the high cost.
2. bypass protection method. This scenario uses transient suppression components (such as TVS, MOV, gas discharge tubes, etc.) will be harmful to the Earth transient energy bypass, the advantage of lower cost, the disadvantage is that protection is limited, only protection of certain transient disturbances within the energy, the duration is not very long, but need to have a good connection to the Earth, it is difficult to implement. It is the practical application of these two programmes combine flexibility, as in Figure 14. In this approach, the isolation of transient disturbance substantially the interface segregation, bypass the protection of isolated interface components are not excessively high transient voltage breakdown.