外文资料PLC

外文翻译原文：The open system merit of ComputerNumerical ControlThe open system merit is the system simple, the cost low, but the shortcoming is the precision is low. The reverse gap, the guide screw pitch error, stop inferiorly can affect the pointing accuracy by mistake. Following several kind of improvements measure may cause the pointing accuracy distinct improvement.1. reverse gap error compensates The numerical control engine bed processing cutting tool and the work piece relative motion is depends upon the drive impetus gear,the guide screw rotation, thus the impetus work floor and so on moves the part to produce moves realizes. As traditional part gear, guide screw although the manufacture precision is very high, but always unavoidably has the gap. As a result of this kind of gap existence, when movement direction change, starts the section time to be able to cause inevitably actuates the part wasting time, appears the instruction pulse to push the motionless functional element the aspect. This has affected the engine bed processing precision, namely the instruction pulse and actual enters for the step does not tally,has the processing error therefore, the split-ring numerical control system all establishes generally has the reverse gap error compensatory function, with by makes up which wastes time the step reverse gap difference compensates is first actual reverse enters for the error, converts the pulse equivalent number it, compensates the subroutine as the gap the output, when the computer judgment appears when instruction for counter motion, transfers the gap to compensate the subroutine immediately, compensates the pulse after the output to eliminate the reverse gap to carry on again normally inserts makes up the movement.2. often the value systematic characteristic position error compensatesA kind of storehouse by transfers for the designer. Like this in the components design stage, the designer only must input the characteristic the parameter, the system direct production characteristic example model: We must save the related characteristic class in the database the structure information, the database table collection are use in saving this part of related information. According to the characteristic type definition need, we defined the characteristic class code table, thecharacteristic class edition information have outstanding shown the characteristic type; Defined the characteristic class structure outstanding to reach the characteristic class the structure; And relates through the components characteristic disposition table and the components characteristic level information. The characteristic level data sheet collection is this components model database design core, has recorded characteristic example information and so on model design, craft. The characteristic structure table has recorded the characteristic geometry structure; The characteristic size table, the characteristic shape position table of limits, the characteristic surface roughness table has recorded the characteristic project semantics quotation; The size table, the shape position table of limits, the surface roughness table saved all components characteristic data message. In the characteristic level, using characteristic ID, geometry principal linkage and so on essential factor ID, size ID, common difference ID, roughness ID carries on the data retrieval. We apply this components information model database under the factory environment some module CAD in the AM integrative system, has realized CAD and the CAPP characteristic information sharing well. Main use ready-made CAD/the CAM software (Unigra phics 1I) carries on the product design and the NC programming in this system, and through carries on two times of developments gains components to this software the size information; At the same time uses the dialogue window which develops voluntarily, lets design the personnel to input other characteristic information alternately, realizes this software and the system sharing database connection. When assistance technological design, the technological design personnel through the procedure inquiry function, inquires the components information from the sharing database which needs, carries on the interactive technological design. Thus has facilitated the CAPP components information acquisition, enhanced the technological design efficiency. When carries on the NC programming using UG, may from the sharing database gain the craft and the manufacture information which needs, carries on various working procedures the knife axle design and the processing simulation establishes an absolute zero spot on the numerical control engine bed, the actual various coordinate axes syzygy completely position error, makes the curve in order to determined compensates the spot. Attempts l to show is an actual position error curve, (error) carries on this curve y-coordinate take the pulse equivalent as the unit the division, makes the horizontal line, each horizontal line and the curve point of intersection namely compensates the spot for the goal. Chart 1 the center 1 to 6 o'clock place position errors for, needs todo reduces the pulse to compensate; But needs to carry on 6 to 9 adds the pulse to compensate in the chart the shadow partially for to compensate the area. Compensates the range of points these to become the error The calibration corrections stores the computer, when work table by zero displacement in position, installs sends out the absolute zero point localization signal in the absolute zero point micros witch, later computer as necessary will send out the goal to compensate to compensate the signal, will carry on the position error to the engine bed to compensate. The cosine generator assigns slide guage initiation signal a electricity and by step of transmission.3. feedbacks compensates the open-loop controlThis system surveys two parts by the open-loop control and the induction synchromesh direct position to be composed. Here position examination does not serve as the position the feedback, but is compensates the feedback as the position error. Its cardinal principle is: Installs the instruction pulse by the engine bed numerical control which CNC sends out, on the one hand the supplies open system, the control step-by-steps the electrical machinery according to the instruction revolution, and the direct drive platen moves, constitutes the open-loop control; On the other hand this instruction pulse supplies the induction synchromesh the measurement system (namely digitally, cosine generator), as position demand signal a by. The work in the warning way induction synchromesh this time not only is the position sensor, also is the comparator, it by, The cosine generator assigns slide guage initiation signal a electricity and by step of transmission.4. conclusionsUnder the CIMS environment the technology which develops unceasingly based on characteristic components information modeling, how enhances the components order of complexity which the characteristic design can complete; How causes question and so on request which the characteristic design adoption trick recognition, the characteristic semantics transforms also to wait for the people to solve. This article introduced the characteristic technology in the components information modeling application, describes this components data model database realization with emphasis; Establishes the components information database system may satisfy the CIMS system well to the letter.译文：数控机床开环控制伺服系统开环系统的优点是系统简单、成本低，但缺点是精度不高。

PLC automatic control system to improve the reliability1. The main reasons for the lower control system reliabilityAlthough the main reason for the decline in industrial control system relia bility and control aircraft PLC itself has high reliability But if the input signal to the PLC Switch mistakes analog signal larger deviations, Output PLC contr ol by the implementing agencies do not require action, which will enable contr ol of mistakes The economic losses caused irreparable. PLC wrong signal to th e scene affect the importation of the main reasons are: 1. Signal transmission l ine caused a short circuit or open circuit (due to mechanical shearing, their agi ng lines connecting dislocation). When the signal transmission line failure, the signal can not be transmitted to the scene PLC, the controlling mistakes. 2, th e mechanical contact tremble, although close contact one scene, but that closed several PLC, Although the increase in the filter circuit hardware, software diff erential increased orders, but because PLC scan cycle is too short, it was possi ble to count, add up. Displacements orders mistake, error control results. 3, the transmitter site and switches their own fault, such as contact connections and Transmitter site reflects the normal work of non-electricity or larger deviations. These same fault control system will not function properly. Impact of implem enting agencies to identify two main reasons: one, the contact is not reliable l oad control actions Although PLC issued a direct action, but did not request e xecutive body movements. 2, starting inverter control, inverter own fault, no co nverter required to bring the electrical work. 3, various electrical valve did not open the solenoid valve is opened, the customs clearance can not place As th e implementing agency did not require action by the PLC control, the system's normal work, the system's reliability. To improve the reliability of the entire c ontrol system, it is necessary to increase the input signal reliability and accura cy of the executive body movements. Otherwise PLC should be able to prompt ly identify problems and suggest ways to use sound and light alarm and otheroperators as soon as possible troubleshooting. Let safe, reliable and correct m anner.2.Designed Fault Alarm SystemSound design fault in the alarm system in automatic control system design, we designed a three-level fault display and warning system. 1 in the control of the control cabinet-level panel set up with the normal operation of the equi pment and troubleshooting instructions light. When the corresponding light-norm al operation of the equipment, the operation of the equipment malfunction indi cator light to the frequency of 1Hz scintillation. Light bulbs to prevent damage to equipment not properly reflect the work, set up a specialized fault reductio n / Test button lights. Continuous system operation any time by more than 3 s econds the button, all beacons should all brightened. If, at this time, there are no instructions on the bright light shows are bad, they should be replaced after the light changed buttons reduction upon the state of the original work and di splay equipment operating status. 2-level fault show large-screen monitors set u p in the center control room, equipment failure, written show faults, process fl ow diagram corresponding equipment flickered in the incident will be recorded in the history of failure. Level 3 indicates fault signal box located in the cent er control room, equipment failure, the acoustic signal boxes will be used. - A larm suggested staff time fault. At fault, the fault will classify some system fai lures is to stop the operation. But some little fault of the system, operating sy stem fault zone, faults can be excluded from the operation. This will greatly re duce the entire system to stop the running time and improve system reliability operating standards.3.Input Signal ReliabilityPLC input signal to the scene to improve the reliability, it is first necessa ry to choose the higher reliability of the transmitter, and various switches. Signal transmission lines to prevent short circuit caused a variety of reasons, disco nnected or have access to. Second, in the process of increasing digital filtering process and increase the credibility of the input signal. Design digital signal f iltering methods are available, input contact at the scene after the one timer. C ontact timing jitter and time based system to determine the response rate, the general in dozens of ms.This can ensure stability in close contact indeed, the o nly other response. Analog filter design procedures are available on the spot fo r sampling analog signal three times D conversion rate and the sampling interv al from the analog signal changes in the rate-determining. 3rd sampling data w ere stored in the data register DT10 and DT11 and DT12. When the last one after the use of data sampling, direct data exchange, data comparison of the m aximum and minimum order removed. The median value of retained as a resul t of sampling DT0 were stored in the data register. In practical application, an d also to extend the sampling of the number of tools to achieve better results. Improve the reliability of signal and can be read into the PLC control system using their own characteristics, signal to determine the relationship between th e degree of credibility. If for liquid level control, known as the size of the tan k, the valve opening into the fluid and the fluid pressure is known. changes in a certain period of highly liquid tank is known about what extent, If given ti me Level PLC great difference in level data and estimates, judgments may be Level Fault, Failure to notify the alarm system operating officer of the Level. Another example is the ultimate protection Tank Level namely, when he switch es to send signals PLC, and the signal is really reliable, in the process of the tank level when we turn signal and the signal, if it also limit Level Meter rea dings position Note that the signal is true; If Level Meter readings not limit lo cation. Level limit switch is the likely transmission of signal failure or fault li nes. Similarly informed by the operator to address the alarm system failure. Be cause of the above methods in the design process, greatly improving the reliab ility of the input signal4.Reliability implementing agenciesWhen the input signal to accurately PLC, PLC enforcement procedures res ults through the implementation of regulatory agencies on-site installations, cont rol. How to ensure that control requirements by implementing agencies, as requ ired when implementing agencies did not work, and how defects? When we ad opt the following measures: Supported by the contactor control when to start o r stop this kind of load contactor coil control.contactor pull reliable start and s top when it contacts for the release of reliable, it is of concern to us. The foll owing procedure is designed to determine the reliability of contact for action. The operating conditions for contacts X0, Y0 for the control coil output X1 P LC input to bring back the contact Auxiliary is always open contact, timer de vices regular contact time than action time. R0 for the creation of the fault po sition, said there was R0 to ON, OFF done for the police to deal with; R0 sa id no failures. Fault with memory function, reduction by the failure to remove the buttons. When the valve opened or closed, according to the valve opening, closing time, delay time to set up, After opening in place or to delay detecti on signal in place, if these signals back to the PLC on time and accurately. N ote valve failure may have done Valve Failure Alarm. Program design as descr ibed below. X2 opened valve, control valve Y1 output time than regular valve opening timer in place, X3 valve in place for the return signal to the valve f ailure R1 spaces. Meanwhile, the export of the switches have intermediate rela y. More important than the intermediate relay can be used to control the move ments of other supplementary contact information feedback to the PLC. Other steps in the logic of user knowledge. Some of the following steps, in fact onl y a more general, you encounter a particular application, it was modified or ad justed. Troubleshooting is the best tool you feel and experience. First, the devi ce onto the program, and will switch hitting RUN position, and then by the fo llowing steps. 1, if the PLC to stop output in some places was encouraging, t he general state of the middle, then you trigger the next operation of signal (i nput, timer, Sichuan line, drum controller). All programming will show that the state of data with self-similar signal. 2, if the input signal, the programming will be shown on the state and input LED module compared the results inconsistent instructions then replace the input module. Found that the expansion into the framework of a number of modules to be replaced, then you replace the module, I/O should be checked cables and expand its links. 3, and if the input state of the LED input module line instructions, instructions it is necessary to compare with the LED input devices (buttons, limit switch, etc.) state. Into t wo different measuring about importation of modules, such as are found, the n eed to replace I/O devices, field wiring or power; Otherwise, the input module to be replaced. 4, as is the signal line Sichuan, no output or output lines and the state of Sichuan, Programming must use to inspect the export-driven logic, and inspection procedures list. From the inspection should be carried out to t he left to find a resolution is not connected to the contact, if there is no card that is imported, on the second and third by-step examination of the input, so lines of Sichuan, according to the 4th and 5th further investigation. Enable pr osecutors to identify the impact of further relay logic operation. 5, if the signa l is the timer, and less than 999.9 parked in the non-zero value, will have to replace the CPU module. 6, if the signal control a counter starting reset contro l logic, then counter signals. Above 2-5 conduct.Troubleshooting equipment SR PLC light inside the aircraft and equipment, beneficial to the entire control system PLC find fault. All programming is the main diagnostic tool, he can easily inserted PLC above. The programmer can observe the entire control system of the state, when you go to find the core o f the PLC control system malfunction. as a habit, you should bring a program mer. Search basic fault order to ask the following questions, based on the reas onable actions found no case-by-case basis. Step-by-step replacement of the SR various modules until the total exclusion fault. All major amendments action pass to complete the replacement module. Apart from a screwdriver and a avo meter, they do not require any special tools, no oscilloscope, High precision v oltage meter or special test procedures. 1, PWR (Power) whether the lights? If not shine, AC power supply in the framework of the voltage input (98-162V AC or 195-252VAC) Checks Supply voltage; DC voltage necessary for the framework, measuring +24 VDC and-0VDC between DC voltage, If not suitable AC or DC power supply, and the problem occurred outside the SR PLC. If A C or DC power supply voltage normal, but the PWR Lamp check fuse, if nec essary, CPU replacement framework. 2, PWR (Power) whether the lights? If br ight, revealed the error code and control code error code definition of the ques tionnaire, as amended accordingly. 3, RUN (running) lights not? If not shine, t he inspection program is not at PRG or LOAD position, or is not a procedura l error. If RUN Lamp, and programming for no flag, or programmer at the R UN mode and no indication of the error code is the need to replace the CPU module. 4, BATT (battery) whether the lights? If bright, the need to replace th e lithium battery. As BATT light is a warning signal, even if the battery volta ge is too low, the procedure may have not been changed. Replace batteries, or to allow inspection procedures PLC test run. If the program has been wrong, the completion of system initialization program, the tapes will be recorded in t he process re-loaded PLC. 5, in the framework of multi-system, if the CPU is working. RUN` Relay can be used to examine several other power work. If n ot closed Relay RUN (resistive state). The above by the first inspection AC or DC power source such as AC or DC power supply is normal and relay disco nnected, Framework will need to be replaced.PLC自动提高控制系统可靠性的方法一、控制系统可靠性降低的主要原因虽然工业控制机和可编程控制器本身都具有很高的可靠性，但如果输入给PLC 的开关量信号出现错误，模拟量信号出现较大偏差，PLC输出口控制的执行机构没有按要求动作，这些都可能使控制过程出错，造成无法挽回的经济损失。

学校名称外文翻译专业：班级学号：学生姓名：指导教师：二〇一一年六月学校名称本科生毕业设计原文1：Programmable logic controllers 译文1：可编程逻辑控制器原文2：Foundation of PLC译文2：PLC基础专业班级：学生姓名：指导教师：学院：2011年6月原文1：Programmable logic controllersProgrammable logic controller(PLC) is eight 10- Year on behalf new generation industry that develop the control equip, and is an automatic control, calculator with the thing that the correspondence technique combine together, and is a the spot equipments for exclusively used foring the industry production line controling. Make the PLC there is characteristics of obvious oneself on the design with the long- term and continuous that circulate because of the special of the complexity, usage environment of the control object: The dependable is high, and the adaptability is wide, and have to correspond by letter the function, and weave the the convenience, construction mold piece . Gather the the control in the modern in the system, the PLC have already become a kind of importance of basic control unit, control the realm the inside in the industry applied the foreground is very and extensive.A programmable logic controller(PLC) is a solid-state devide used to control machine motion or process operation by means of a stored program. The PLC sends output control signals and receives input signals through input/output (I/O) devices.A PLC controls outputs in response to stimuli at the inputs according to the logic prescribed by the stored program.The inputs are made up of limit switches,pushbuttons,thumbwheels, switches,pulses,analog signals,ASCII serial data,and binary or BCD data from absolute position encoders.The outputs are voltage or current levers to drive end devices such as lolenids,motor staters,relays,lights,and so on.Other output devices such include analog devices,digital BCD displays,ASCII compatible devices,servo variable-speed drives,and even computers.Programmable controllers were developed(circa in 1968) when General Motors Corp,and other automobile manufacturers were experimenting to see if there might be an alterantive to scrapping all their hardwired control panels of machine tools and other production equipment during a model changeover.This annual tradition was necessary because rewiring of the panels was more expensive than buying new oens.The automotive companies approached a number of control equipment manufacturers and asked them to develop a control system that would have a longer productive life without major rewiring,but would still be understandable to and repairable by plant personnel.The new product wa namd a“programmable controller”．The processor part of the PLC contains a central processing unit and memory.The central proce ssing unit(CPU) is the“trafficdirector”of the processor,the memory stores ing into the processor are the electrical signals from the input devices，as conditioned by the input module to voltage levels acceptable to processor logic．The processor scans the state of I／O and updates outputs based on instructions stored in the memory of the PLC．For example，the processor may be programmed so that if an input connected to a limit switch is true(1imit switch closed),then a corresponding output wired to an output module is to be energized．This output might be asolenoid for example．The processor remembers this command through its memory and compares on each scan to see if that limit is, in fact ,closed. If it is closed, the processor energizes the solenoid by turning on the output module.The output device, such as a solenoid or motor stater,is wired to an output mofule’s terminal,and itreceives its shift signal from the processor, in effect the peocessor is performing a long and complicated series of logic decisions. The PLC performs such decisions sequentially and in accordance with the stored program.similarly, analog I/O allows the processor to make decisions based on the magnitude of a signal, rather than just if is on or off.For example,the processor may be programmes toencrease or decrease the steam flow to a boiler(analog output) based on a comparison of the actual temperature in the boiler(analog input) to the desired temperature. this is often performed by utilizing the built-in PID(proportional,integral,derivative) capabilities of the processor.Proper power to the programmable controller is critical. Today’s systems are available in a wide variety of electrical configurations. Virtually all are designed for use in single-phase power systems, and most are now beginning to be offered with the optional ability to operate in a DC supply environment. AC designs are offered in either single voltage supplies, such as 115 or 230V AC; while some can be configured as either through a selection made on the power supply. Proper grounding of the power supply connection is required for a safe installation. Some programmable controller designs have individual grounding connections from rack to face- plates and other system components, so care must be taken to follow well electrical practice in system grounding during electricalinstallation. In certain applications, a 24 or 120 V DC power supply is required. This is common for installations that axe made where no AC power is available, such as remote electrical generation stations. It is also found where AC power is unreliable and where loss of control is considered an unacceptable situationEven the best of today' s well-designed and manufactured programmable controllers require occasional preventative maintenance and repair. This section looks at some of the tools provided by the manufacturer and techniques for general maintenance.Most of the medium- and large-sized programmable controller systems available today are designed to be maintained by individuals with a wide variety of skills, without the benefit of in-depth formal training of this piece of equipment. This is accomplished in the design by providing individual modules of functionality installed in a chassis serviced from the front (all module types including power supplies). Front access is critical to proper maintenance. This allows easy inspection and replacement of the suspected bad module. Module health is determined by inspecting the LED indicators normally provided on the front of each module. Typical indicators will be on or off depending on the design and individual condition of the module in question. Various CPU and I/O modules will have indicators showing I/O control communications status, memory integrity, power supply tolerance check, scan integrity, and others. On future controller designs, and even today on a few systems, it is likely that English language messages will be displayed on the controller advising the user or maintenance personnel that a particular failure has occurred and recommended actions to take.The modular design and diagnostic indicators are, of course, important, but would be quite useless without well designed documentation provided by the manufacturer for the programmable controller system in question. Proper documentation will have sections dedicated to each major subsystem including CPU, I/O, and programming device. Each should explain in depth the stop-by-stop inspection of the system. All possible combinations of failure mode should be listed, along with suggested actions for repair. This will most often involve only the substitution of a re- placement board for the suspected failed unit. The user is urged to purchase a set of spare modules for the system in question as recommended by the manufacturer. This is normally, at a minimum, a single replacement module for each CPU and programming device serviceable module, and spare I/O modules equal to 10% of the number in the system.Because a PLC is “software based”,its control logic functions can be changed byreprogramming its memory. Keyboard programming devices facilitate entry of the revised program, which can be designed to cause an existing machine or process to operate in a different sequence or to respond to different levels of, or combinations of stimuli .Hardware modifications are needed only if additional, changed, or relocated input/output devices are involved.Programmable controller memory is formatted into bits, bytes, and words of memory.A bit is a single storage element for either a zero or a one. A byte consists of eight bits, and a word (normally) consists of 16 bits, or two bytes. Some systems still use a word length of eight bits, but most have adopted a 16 bit word, even though they may use an 8 bit microprocessor.Depending on the specific design of the programmable controller, it will have a stated memory capacity. This is an indication, although not the only one, of the capability and power of the system. Medium and large controllers are normally expandable from one memory size to their maximum size. Small controllers are normally fixed in their memory size. Size of the memory capacity must be examined relative to the word size ( 8 bit or 16 bit) and utilization. While it is clear that twice the information can be stored in a 16 bit word than in an 8 bit word, it may not be immediately clear that some controllers utilize memory more efficiently than others. For example, a normally open contact and its associated reference address (e.g. Input 1), may use in 8 bit byte each for storage. Combined, they consume one 16 bit word. Some controllers may use more memory than this for these instructions or others. In a large program, these inefficiencies can build on each other to cause a poor utilization of the system memory. A careful analysis of the various programmable controller models is required to assess utilization efficiency. Normal practice calls for an additional 20% - 40% of memory size to be specified to allow for modifications and later expansion. This analysis, combined with knowledge of the application needs, will allow for an intelligent choice of programmable controller.In fine, PLC conduct and actions the spot control equipments, can dependable，accurately complete the control the operation, and can pass with upper grade work machine correspondence, constitute the distribute type the system to complete to control the industry equip. system control request, is a modern industry control the inside compare forerunner’s control project, and apply the foreground to is extensive.译文1：可编程逻辑控制器可编程逻辑控制器（PLC）是八十年代发展起来的新一代工业控制装置，是自动控制、计算机和通信技术相结合的产物，是一种专门用于工业生产过程控制的现场设备。

Introductions of PLC and MCUA PLC is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs .The user enters a program, usually via software or programmer that gives the desired results.PLC are used in many “real world〞applications. If there is industry present, chances are good that there is a PLC present. If you are involved in machining, packaging, material handling, automated assembly or countless other industries, you are probably already using them. If you are not, you are wasting money and time. Almost any application that needs some type of electrical control has need for PLC.For example, let’s assume that when a switch turns on we want to turn a solenoid on for 5 seconds and then turn it off regardless of how long the switch is on for. We can do this with a simple external timer. What if the process also needed to count how many times the switch individually turned on? We need a lot of external counters.As you can see, the bigger the process the more of a need we have for a PLC. We can simply program the PLC to count its inputs and turn the solenoids on for the specified time.We will take a look at what i s considered to be the “top 20〞PLC instructions. It can be safely estimated that with a firm understanding of there instructions one can solve more than 80% of the applications in existence.That‘s right, more than 80%! Of course we’ll learn more than jus t these instructions to help you solve almost ALL your potential PLC applications.The PLC mainly consists of a CPU, memory areas, and appropriate circuits to receive input/output data, as shown in Fig. 19.1 We can actually consider the PLC to be a box full of hundreds or thousands of separate relays, counters, timer and date storage locations. Do these counters, timers, etc. really exist? No, they don’t “physically〞exist but rather they are simulated and can be considered software counters, timers, etc. These internal relays are simulated through bit locations in registers.What does each part do?INPUT RELAYS-(contacts) These are connected to the outside world. They physically exist and receive signals from switches, sensors, etc... Typically they are not relays but rather they are transistors.INTERNAL UTILITY RELAYS-(contacts) These do not receive signals from the outside world nor do they physically exist. They are simulated relays and are what enables a PLC to eliminate external relays. There are also some special relays that are dedicated to performing only one task. Some are always on while some are always off. Some are on only once during power-on and are typically user for initializing data what was stored.COUNTERS These again do not physically exist. They are simulated counters and they can be programmed to count pulses. Typically these counters can count up, down or both up and down. Since there are simulated, they are limited in their counting speed. Some manufacturers also include high-speed counters that are hardware based. We can think of these as physically existing. Most timers these counters can count up, down or up and down.TIMERS These also do not physically exist. They come in many varieties and increments. The most common type is an on-delay type. Other include off-delay and both retentive and non-retentive types. Increments vary from 1ms through 1s.OUTPUT RELAYS-(coil) These are connected to the outside world. They physically exist and send on/off signals to solenoids, lights, etc… They can be transistors, relays, or triacs depending upon the model chosen.DATA STORAGE-Typically there are registers assigned to simply store data. There are usually used as temporary storage for math or data manipulation. They can also typically be user power-up they will still have the same contents as before power war removed. Very convenient and necessary!A PLC works by continually scanning a program. We can think of this scan cycle as consisting of 3 important steps, as shown in Fig. There are typically more than 3 but we can focus on the important parts and not worry about the others. Typically the others are checking the system and updating the current and timer values.Step 1-CHECK INPUT STATUS-First the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input on? How about the second input? How about the third…It records this data into its memory to be used during the next step.Step 2-EXECUTE PROGRAM-Next the PLC executes your program one instruction at a time. Maybe your program said that if the first input was on then it should turn on the first output. Since is already knows which inputs are on/off from the previous step, it will be able to decide whether the first output should be turned onbased on the state of the first input. It will store the execution results for use later during the next step.Step 3-UPDATE OUTPUT STSTUS-Finally the PLC updates the status of outputs. It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true.After the third step the PLC goes back to step one and repeats the steps continuously. One scan time is defined as the time is takes to execute the 3 steps listed above. Thus a practical system is controlled to perform specified operations as desired.The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8Kbytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pin-out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications.The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight TTL inputs. When is written to port 0 pins, the pins can be used as high-impedance inputs.Port 0 can also be configured to be the multiplexed lowered address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups.Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification.Port 1 is an 8-bit bidirectional I/O port with internal Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (I IL) because of the internal pull-ups.In addition, P1.0 and P1.1 can be configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2 trigger input (P1.1/T2EX).PLC和微处理器简介PLC(可编程逻辑控制器)是极限控制中为代替必要的继电器时序电路而创造的一种设备。