1、 PLC technique discussion and future developmentK. Begain, M. ErmelChair for Telecommunications, Dresden University of Technology,01062 Dresden, GermanyAbstract: Programmable Logic Controllers (PLC), a computing device invented by Richard E.Morley in 1968, have been widely used in industry including
2、 manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC placed the hardwired logic with soft-wired logic or so-called relay ladder logic(RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configura
3、tion time from 6 months down to 6 days Moody and Morley,1999.Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in hars
4、h environments. Moreover, according to a study on the PLC market of Frost and Sullivan 1995, an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping.
5、The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time.Key Words：PLC ，performance ，market1 IntroductionAlong with the development of the ages, the technique that is nowadays is also gradually perfect, the competition plays more more str
6、ong; the operation that list depends the artificial has already cant satisfied with the current manufacturing industry foreground, also cant guarantee the request of the higher quantity and high new the image of the technique business enterprise.The people see in produce practice, automate brought t
7、he tremendous convenience and the product quantities for people up of assurance, also eased the personnels labor strength, reduce the establishment on the personnel. The target control of the hard realization in many complicated production lines, whole and excellent turn, the best decision etc., wel
8、l-trained operation work, technical personnel or expert, governor but can judge and operate easily, can acquire the satisfied result. The research target of the artificial intelligence makes use of the calculator exactly to carry out, imitate these intelligences behavior, moderating the work through
9、 persons brain and calculators, with the mode that persons machine combine, for resolve the very complicated problem to look for the best pathWe come in sight of the control that links after the electric appliances in various situation, that is already the that time generation past, now of after use
10、 in the mold a perhaps simple equipments of grass-roots control that the electric appliances can do for the low level only;And the PLC emergence also became the epoch-making topic, adding the vivid software control through a very and stable hardware, making the automation head for the new high tide.
11、2 PLC characteristics and containment2.1 The PLC biggest characteristicsThe PLC biggest characteristics lie in: The electrical engineering teacher already no longer electric hardware up too many calculationses of cost, as long as order the importation that the button switch or the importation of the
12、 sensors order to link the PLC up can solve problem, pass to output to order the conjunction contact machine or control the start equipments of the big power after the electric appliances, but the exportation equipments direct conjunction of the small power can.Figure 1. Open frame PLC2.2 PLC intern
13、al containmentPLC internal containment have CPU, and take to have an I/ O for expand of exterior to connect a peoples address and saving machine three big pieces to constitute, CPU core is from an or many is tired to add the machine to constitute, mathematics that they have the logic operation abili
14、ty, and can read the procedure save the contents of the machine to drive the homologous saving machine and I/ Os to connect after pass the calculation; The I/ O add inner part is tired the input and output system of the machine and exterior link, and deposit the related data into the procedure savin
15、g machine or data saving machine; The saving machine can deposit the data that the I/ O input in the saving machine, and in work adjusting to become tired to add the machine and I/ Os to connect, saving machine separately saving machine RAM of the procedure saving machine ROM and datas, the ROM can
16、can do deposit of the data permanence in the saving machine, but RAM only for the CPU computes the temporary calculation usage of hour of buffer space. Figure 2. PLC input and output circuits2.3 PLC advantageThe PLC anti- interference is very and excellent, our root need not concern its service life
17、 and the work situation bad, these all problems have already no longer become the topic that we fail, but stay to our is a concern to come to internal resources of make use of the PLC to strengthen the control ability of the equipments for us, make our equipments more gentle.PLC language is not we i
18、magine of edit collected materials the language or language of Cs to carry on weaving the distance, but the trapezoid diagram that the adoption is original after the electric appliances to control, make the electrical engineering teacher while weaving to write the procedure very easy comprehended th
19、e PLC language, and a lot of non- electricity professional also very quickly know and go deep into to the PLC.3 HMIIs PLC one of the advantage above and only, this is also one part that the people comprehend more and easily, in a lot of equipmentses, the people have already no longer hoped to see to
20、o many control buttons, they damage not only and easily and produce the artificial error easiest, small is not a main error perhaps you can still accept; But lead even is a fatal error greatly is what we cant is tolerant of. New technique always for bringing more safe and convenient operation for us
21、, make we a lot of problems for face on sweep but light, do you understand the HMI? Says the HMI here you basically not clear what it is, also have no interest understanding, change one inside text explains it into the touch to hold or man-machine interface you knew, it combines with the PLC to our
22、larger space.HMI the control not only only is reduced the control press button, increase the vivid of the control, more main of it is can sequence of, and at can the change data input to output the feedback with data, control in the temperature curve of imitate but also can keep the manifestation of
23、 view to come out. And can write the function help procedure through a plait to provide the help of various what lies in ones power, the one who make operate reduces the otiose error. Currently the HMI factory is also more and more, the function is also more and more strong, the price is also more a
24、nd more low, the noodles of the usage are wide more and more. The HMI foreground can say that think to be good very.4 PLC correspondence and data transmissionAt a lot of situations, the list is is a smooth movement that cant guarantee the equipments by the control of the single machine, but pass the
25、 information exchanges of the equipments and equipments to attain the result that we want. For example fore pack and the examination of the empress work preface, we will arrive wrapping information feedback to examine the place, and examine the information of the place to also want the feedback to p
26、acking. Pass the information share thus to make both the chain connect, becoming a total body, the match of your that thus make is more close, at each other attain to reflect the result that mutually flick.The PLC correspondence has already come more more body now its value, at the PLC and correspon
27、dence between PLCs, can pass the communication of the information and the share of the datas to guarantee that of the equipments moderates mutually, the result that arrive already to repair with each other. Data conversion the adoption RS232 between PLC connect to come to the transmission data, but
28、the RS232 pick up a people and can guarantee 10 meters only of deliver the distance, if in the distance of 1000 meters we can pass the RS485 to carry on the correspondence, the longer distance can pass the MODEL only to carry on deliver.The PLC data transmission is just to be called a form to it in
29、a piece of and continuous address that the data of the inner part delivers the other party, we, the PLC of the other party passes to read data in the watch to carry on the operation. If the data that data in the watch is a to establish generally, that is just the general data transmission, for examp
30、le today of oil price rise, I want to deliver the price of the oil price to lose the oil ally on board, that is the share of the data; But take data in the watch for an instruction procedure that controls the PLC, that had the difficulty very much, for example you have to control one pedestal robot
31、to press the action work that you imagine, you will draw up for it the form that a procedure combine with the data sends out to pass by.Figure 3. PLC connection with experiments board.4.1 Form of information transmission4.1.1 Simplex and DuplexThe form that information transport contain Simplex, the
32、 Half duplex and the Full duplex.The meaning of the Simplex also is to say both, a can send out only, but a can receive only, for example a spy he can receive the designation of the superior only, but cant give the superior reply; Half duplex is also 2 and can can send out similar to accept the data
33、, but cant send out and accept at the same time, for example when you make a phone call is to cant answer the phone, the other party also; But the Half duplex is both can send out and accept the data, and can send out and accept at the same time. Be like the Internet is a typical example.4.1.2 Synch
34、ronous and AsynchronousThe process that information transport also has synchronous and asynchronous: The data line and the clock lines are synchronous when synchronous meaning lie in sending out the data, is also the data signal and the clock signals to be carry on by the CPU to send out at the same
35、 time, this needs to all want the specialized clock signal each other to carry on the transmission and connect to send, and is constrained, the characteristics of this kind of method lies in its speed very quick, but correspond work time of take up the CPU and also want to be long oppositely, at the
36、 same time the technique difficulty also very big. Its request lies in canting have an error margins in a datas deliver, otherwise the whole piece according to compare the occurrence mistake, this on the hardware is a bigger difficulty. Applied more and more extensive in some appropriative equipment
37、ses, be like the appropriative medical treatment equipments, the numerical signal equipments.etc., in compare the one data deliver, its result is very good.And asynchronous is an application the most extensive, this receive benefit in it of technique difficulty is opposite and want to be small, at t
38、he same time not need to prepare the specialized clock signal, its characteristics to lie in, its data is partition, the long-lost send out and accept, be the CPU is too busy of time can grind to a stop sex to work, also reduced the difficulty on the hardware, the data throw to lose at the same time
39、 opposite want to be little, we can pass the examination of the data to observe whether the data that we send out has the mistake or not, be like strange accidentally the method, tired addition and eight efficacies method etc., can use to helps whether the data that we examine to send out have or no
40、t the mistake occurrence, pass the feedback to carry on the discriminator.4.1.3 Parallel and SerialA line of transmission of the information contain a string of and combine the cent of: The usual PLC is 8 machines, certainly also having 16 machines. We can be an at the time of sending out the data a
41、 send out to the other party, also can be 88 send out the data to the other party, an and 8 differentiationses are also the as that we say to send out the data and combine sends out the data. A speed is more and slowly, but as long as 2 or three lines can solve problem, and can use the telephone lin
42、e to carry on the long range control. But combine the oscular transmission speed is very quick of, it is a string of oscular of 25600%, occupy the advantage in the short distance, the in view of the fact TTL electricity is even, being limited by the scope of one meter generally, it combine unwell us
43、ed for the data transmission of the long pull, thus the cost is too expensive.Under a lot of circumstances we are total to like to adopt the string to combine the conversion chip to carry on deliver, under this kind of circumstance not need us to carry on to depositted the machine to establish too a
44、nd complicatedly, but carry on the data exchanges through the data transmission instruction directly, but is not a very viable way in the correspondence, because the PLC of the other party must has been wait for your data exportation at the time of sending out the data, it cant do other works.4.2 In
45、terruptWhen you are reading the book, you hear someone knock on door, you stop to start up of affair, open the door and combine to continue with the one who knock on door a dialogue, the telephone of this time rang, you signal hint to connect a telephone, after connecting the telephone through, retu
46、rn overdo come together knock on door to have a conversation, after dialogue complete, you continue again to see your book, this kind of circumstance we are called the interruption to it, it has the authority, also having sex of have the initiative, the PLC had such function .Its characteristics lie
47、 in us and may meet the urgently abrupt affairs in the operation process of the equipments, we want to stop to start immediately up of work, the whereabouts manages the more important affair, this kind of circumstance is we usually meet of, PLC while carry out urgent mission, total will keep the cur
48、rent appearance first, for example the address of the procedure, CPU of tired add the machine data etc., be like to to stick down which the book that we see is when we open the door the page or simply make a mark, because we treat and would still need to continue immediately after book of see the be
49、hind. The CPU always does the affair that should do according to our will, but your mistake of give it an affair, it also would be same to do, this we must notice.The interruption is not only a, sometimes existing jointly with the hour several inside break, break off to have the preferred Class, they will carry out the interruption of the higher Class according to persons request. This kind of breaks off the medium interruption to also became to break off the set. The Class
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