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1、此文档是毕业设计外文翻译成品（ 含英文原文+中文翻译），无需调整复杂的格式！下载之后直接可用，方便快捷！本文价格不贵,也就几十块钱！一辈子也就一次的事！外文标题：Introductions of PLC and MCU外文作者：Sunita Chandrasekaran文献出处: 2018 IEEE International Parallel & Distributed Processing Symposium Workshops (如觉得年份太老，可改为近2年，毕竟很多毕业生都这样做)英文1357单词，8022字符(字符就是印刷符)，中文2327汉字。（如果字数多了，可自行删减，大多数学校
2、都是要求选取外文的一部分内容进行翻译的。）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 softw
3、are 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 proba
4、bly 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, lets 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
5、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 c
6、ount its inputs and turn the solenoids on for the specified time.We will take a look at what is 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.Thats right, mo
7、re than 80%! Of course well learn more than just 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 f
8、ull of hundreds or thousands of separate relays, counters, timer and date storage locations. Do these counters, timers, etc. really exist? No, they dont “physically” exist but rather they are simulated and can be considered software counters, timers, etc. These internal relays are simulated through
9、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 rec
10、eive 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
11、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 limi
12、ted 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.
13、 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 transi
14、stors, 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 powe
15、r 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.19.2 There are typically more than 3 but we can focus on the important parts and not worry about the others. Typically the o
16、thers 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 thirdIt 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.
