毕业设计论文外文文献翻译中英文对照plc发展和市场条件

毕业设计论文外文文献翻译中英文对照plc发展和市场条件内容摘要：

ut also through manual programmers (consoles). This practically means that each PLC controller can programmed through a puter if you have the software needed for programming. Today’s transmission puters are ideal for reprogramming a PLC controller in factory itself. This is of great importance to industry. Once the system is corrected, it is also important to read the right program into a PLC again. It is also good to check from time to time whether program in a PLC has not changed. This helps to avoid hazardous situations in factory rooms (some automakers have established munication works which regularly check programs in PLC controllers to ensure execution only of good programs). Almost every program for programming a PLC controller possesses various useful options such as: forced switching on and off of the system input/outputs (I/O lines), program follow up in real time as well as documenting a diagram. This documenting is necessary to understand and define failures and malfunctions. Programmer can add remarks, names of input or output devices, and ments that can be useful when finding errors, or with system maintenance. Adding ments and remarks enables any technician (and not just a person who developed the system) to understand a ladder diagram right away. Comments and remarks can 无 锡 职 业 技 术 学 院 毕业设计说明书（英文翻译） 4 even quote precisely part numbers if replacements would be needed. This would speed up a repair of any problems that e up due to bad parts. The old way was such that a person who developed a system had protection on the program, so nobody aside from this person could understand how it was done. Correctly documented ladder diagram allows any technician to understand thoroughly how system functions. Electrical supply is used in bringing electrical energy to central processing unit. Most PLC controllers work either at 24 VDC or 220 VAC. On some PLC controllers you’ll find electrical supply as a separate module. Those are usually bigger PLC controllers, while small and medium series already contain the supply module. User has to determine how much current to take from I/O module to ensure that electrical supply provides appropriate amount of current. Different types of modules use different amounts of electrical current. This electrical supply is usually not used to start external input or output. User has to provide separate supplies in starting PLC controller inputs because then you can ensure so called “pure” supply for the PLC controller. With pure supply we mean supply where industrial environment can not affect it damagingly. Some of the smaller PLC controllers supply their inputs with voltage from a small supply source already incorporated into a PLC. 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 a need for a PLC. 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. First PLC controllers were simple devices. They connected inputs such as switches, digital sensors, etc, and based on internal logic they turned output devices on or off. When they first came up, they were not quite suitable for plicated controls such as temperature, position, pressure, etc. However, throughout years, makers of PLC controllers added numerous features and improvements. Today’s PLC controller can handle highly plex tasks such as position control, various regulations and other plex applications. The speed of work and easiness of programming were also improved. Also, modules for special purposes were developed, like munication modules for connecting several PLC controllers to the . Today it is difficult to imagine a task that could not be handled by a PLC. Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one of the microcontrollers. Aforetime these were 8bit microcontrollers such as 8051, and now these are 16and 32bit microcontrollers. Unspoken rule is that you’ll find mostly Hitachi and Fujisan microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care of munication, interconnectedness among other parts of PLC controllers, program execution, memory operation, overseeing input and setting up of an output. PLC controllers have plex routines for memory checkup in order to ensure that PLC memory was not damaged (memory checkup is done for safety reasons).Generally speaking, CPU unit makes a great number of checkups of the PLC controller itself so eventual errors would be discovered early. You can simply look at any PLC controller and see that there are several indicators in the form. of light diodes for error signalization. System memory (today mostly implemented in FL。