1、Plc SynopsisCentral Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one ofthe microcontrollers. Aforetime these were 8-bit microcontrollers such as 8051, and nowthese are 16-and 32-bit microcontrollers. Unspoken rule is that youll find mostly Hitachiand Fujicu microcont
2、rollers in PLC controllers by Japanese makers, Siemens in Europeancontrollers, and Motorola microcontrollers in American ones. CPU also takes care ofcommunication, interconnectedness among other parts of PLC controllers, programexecution, memory operation, overseeing input and setting up of an outpu
3、t. PLCcontrollers have complex routines for memory checkup in order to ensure that PLCmemory was not damaged (memory checkup is done for safety reasons).Generallyspeaking, CPU unit makes a great number of check-ups of the PLC controller itself soeventual errors would be discovered early. You can sim
4、ply look at any PLC controller andsee that there are several indicators in the form. of light diodes for error signalization.System memory (today mostly implemented in FLASH technology) is used by a PLC fora process control system. Aside form. this operating system it also contains a userprogram tra
5、nslated forma ladder diagram to a binary form. FLASH memory contents canbe changed only in case where user program is being changed. PLC controllers wereused earlier instead of PLASH memory and have had EPROM memory instead of FLASHmemory which had to be erased with UV lamp and programmed on program
6、mers. Withthe use of FLASH technology this process was greatly shortened. Reprogramming aprogram memory is done through a serial cable in a program for application development.User memory is divided into blocks having special functions. Some parts of a memoryare used for storing input and output sta
7、tus. The real status of an input is stored either as“1”or as “0”in a specific memory bit/ each input or output has one corresponding bit inmemory. Other parts of memory are used to store variable contents for variables used inused program. For example, time value, or counter value would be stored in
8、 this part ofthe memory.PLC controller can be reprogrammed through a computer (usual way), but alsothrough manual programmers (consoles). This practically means that each PLC controllercan programmed through a computer if you have the software needed for programming.Todays transmission computers are
9、 ideal for reprogramming a PLC controller in factoryitself. This is of great importance to industry. Once the system is corrected, it is alsoimportant to read the right program into a PLC again. It is also good to check from time totime whether program in a PLC has not changed. This helps to avoid h
10、azardous situationsin factory rooms (some automakers have established communication networks whichregularly check programs in PLC controllers to ensure execution only of good programs).Almost every program for programming a PLC controller possesses various usefuloptions such as: forced switching on
11、and off of the system input/outputs (I/O lines),program follow up in real time as well as documenting a diagram. This documenting isnecessary to understand and define failures and malfunctions. Programmer can addremarks, names of input or output devices, and comments that can be useful when findinge
12、rrors, or with system maintenance. Adding comments and remarks enables anytechnician (and not just a person who developed the system) to understand a ladderdiagram right away. Comments and remarks can even quote precisely part numbers ifreplacements would be needed. This would speed up a repair of a
13、ny problems that comeup due to bad parts. The old way was such that a person who developed a system hadprotection on the program, so nobody aside from this person could understand how it wasdone. Correctly documented ladder diagram allows any technician to understandthoroughly how system functions.E
14、lectrical supply is used in bringing electrical energy to central processing unit. MostPLC controllers work either at 24 VDC or 220 VAC. On some PLC controllers youll findelectrical supply as a separate module. Those are usually bigger PLC controllers, whilesmall and medium series already contain th
15、e supply module. User has to determine howmuch current to take from I/O module to ensure that electrical supply provides appropriateamount of current. Different types of modules use different amounts of electrical current.This electrical supply is usually not used to start external input oroutput. U
16、ser has to provide separate supplies in starting PLC controllerinputs because then you can ensure so called “ pure” supply for the PLCcontroller. With pure supply we mean supply where industrial environmentcan not affect it damagingly. Some of the smaller PLC controllers supplytheir inputs with volt
17、age from a small supply source already incorporatedinto a PLC二 Opening and based on the industry PC controlThe PLC manufacturer already started to gaze at the formidable impact which brings basedon the industry PC control technology. Some experts even believed that the new commercialactivity brings
18、new technical and the opening technology standard will bury traditional PLC. ThePLC manufacturer believed that although has the massive PLC control device in the industry fieldinstallation, but they still needed to unite the labor to control the software company, with the aimof developing them based
19、 on the industry PC process control software.Indeed, several years ago have the new old PLC mix use obviously in the industry scene thesituation, the industrial user can not but simultaneously study the related new old knowledge, eveneach other profits from the study. The majority PLC manufacturers
20、have provided the soft logicand one kind of service platform merely for the industrial user.In the high-end application aspect, very difficult to further differentiate the PLC controlsystem and between the industry PC control systems difference, because this both have used thesimilar type microproce
21、ssor and the memory chip. Makes an analogy vividly, if you forgetindustry PC and in the PLC these words and expressions wording meaning, then can observe inthe box is some basic computer hardware technology exactly, we observe are actually these basicstrokes complication and the mixture, these techn
22、ologies are combined effectively in the controlsystemMoreover, uses the opening control the reason is the system functionintegration need at the same time, on the other hand is also because someindustrial user makes excessive demands the result excessively to thefunction. If can give the high value,
23、 can obtain the more basic strokesknowledge. The PLC manufacturer concentrates the systemfunctionalization, but the industrial user concentrates the systemapplication. The people may see that future trend of development will befurther integrates more functions to a control box. Will therefore lookli
24、ke the sequential control and process control such event will selectthe functionalization method to carry on processing, other elephantmotion control and so on can also share in the same control structuresystem.May believe that the PLC technology will continue to the open style control system direct
25、ionto shift, particularly based on industry PC control system. The latter except, in the flexible aspecthas outside the entirely different superiority compared to traditional PLC, but also has other merits,like can reduce the system to put in the market the cycle, reduces the system investment expen
26、ses,enhances from the factory first floor to the enterprise office automation data message mobileefficiency and so on.Already obtained the very good solution about the industry PC control systems real-timeresponse question, perhaps its main thing still hid behind the technology, but lacks thecorresp
27、onding track record. As for PLC, ruggedness is one of its main features, this already hadthe quite many track records to confirm. The industrial user still very carefully treated PLC, theyare doing the different technical test work to PLC. When uses one kind of new technology, theindustrial user nee
28、ds to consider the question is must take the big risk, simultaneously needs toconsider that can bring how many opportunities and the income to its commercial activity.But the industrial user believed not completely the open style control system bringsadvantage. Along with the technical further devel
29、opment, they start to downplay these ideologicalconcept gradually. The industrial user is being balanced uses the risk which the new technologyexists and the income which brings for theirs commercial activity, in order to will provide theeffective safeguard for presents decision-making.The industry
30、PC technology has provided many functions, can strengthen PLC the functioncharacteristic, cooperates the processor including the Inner Tibet video frequency and the highspeed floating point digit. Although Microsoft Corporation has not promoted further this functioncharacteristic plan, but new Windo
31、ws CE 3.0 can definitely satisfy the process control well theneed.Some time ago, Siemens Corporation announced a set newly based on the open style controlsystems software product, namely 3.0 edition SIMATIC WinAC (Windows automation center).WinAC is based on Windows NT, with SIMATIC S7 PLC compatibl
32、e suiting in industry PCcontrol system solution. WinAC 3.0 provided had the high integration rate Profibus field bus localarea networks connection performance, as well as long-distance programming. In addition, it alsointegrated for the scene control device localization has provided one kind of new
33、DeviceNet theI/O device driver, uses in DeviceNet which connected installs I/O equipment.The Steeplechase software company has also promoted set of supports are sturdy and healthywhen process control embedded Windows the NT operating system interface unit. This partfurther unified Steeplechase Corpo
34、ration to use the SBS technology and to move was sturdy andhealthy in Windows NT environment industry Compact PCI when the control software. Now, theSteeplechase Corporations visualization logic controller already promoted to 5.0 editions. Thiscontroller suits in Windows NT 4.0 and the Windows 20,00
35、2 kind of operating systems, itsreal-time engine can direct and ordinary Ethernet and TCP/IP integrates in together. 5.0 editionscontrollers have used one kind of enlargement mode OPC server driver, thus has the quickerrunning rate compared to the beforehand edition. Other characteristics also inclu
36、de the new OInetwork characteristic, as well as can let industrial user design the richly colorful dynamic graphpicture and so on.Transysoft Corporation had promoted the new edition ISaGRAF series industrial controlconfiguration software package recently, namely ISaGRAF PRO, it is based on the IEC 6
37、1131-3international standards, and independence in any hardware platform soft logical automationcontrol software package. In a network process control system environment, this software packagecan apply in many kinds of configurations and the distributional control systems development, ithas containe
38、d a set of development kit, the application procedure working platform, as well ascorresponding “hypothesized machine” when movement goal. When this movement the goal canmove in various hardware platform.The CTC automation Engineering firm had already issued set of new control softwarepackage Machin
39、eLogic PCLC (industry PC logic controller), this software may let industry PC actPLC the role, and was still maintaining the industry PC function characteristic. This software cancomplete the control task which PLC determined, and the program time is equally quick, in 1 ms;Can also the simultaneous
40、working multi-duty work, but cannot simultaneously surpass 16 controlduties. One kind has the priority and the multitasking essence mechanism is maintaining to eachcontrol duty track, guaranteed that the control duty can obtain the highest priority. This softwarecan move the complete 5 kind of IEC 6
41、1131-3 standard program design language and the PIDcontrol procedure, supports two types the I/O control devices. One kind is looks like Profibus andDeviceNet and so on such field bus I/O equipment; Another kind is looks like ISA and PC/104such industry PC the I/O template. Moreover, this software h
42、as also provided to control systemsonline edition configuration function. The procedure may 95/98 and under Windows NT developsin Windows and moves, but can also carry out under RTXDOS.SoftPLC Corporation also provided one kind of labor to control software product Tealware,some people were called as
43、 very vividly this kind of software product are putting on industry PCclothes PLC. These installed on supports control system already had the small PLC form factor,but the SoftPLC Corporations control software was already inserted to CPU. The Tealwaresoftware can satisfy each type industrial user th
44、e need, from small, single plane system tolarge-scale, scattered multi-control workstation application. Its characteristic including entireseries I/O module, Inner Tibet Ethernet and industry serial communication connection.Recently, Tealware the software already promoted to 2.3 editions. And, the c
45、ontrol softwarehas provided in fact the infinite trapezoidal chart logical control step the foreword, simultaneouslyallows to have surpasses 1,000,000 characters the data sheets; Many OI/SCADA applicationconnection; The Inner Tibet Java engine and the FTP server use in the long-distance maintenancea
46、nd the management; Support user compile C, C, Java procedure and device driver; Suits uses inthe embedded Web server; Programming online movement pattern; Firm I/O module supportability and many other standard PLC function; May move, or is A-B Corporations PLC- whichthe process which inputs transforms
