外文翻譯--plc控制系統(tǒng)設(shè)計(jì)的要點(diǎn)-plc設(shè)計(jì)-文庫吧
2025-04-17 08:23 本頁面
【正文】 r year by 1990 and is still growing. Even the machine tool industry, where pute numerical controls (CNCs) have been used in the past, is using PLCs. PLCs are also used extensively in building energy and security control systems. Other nontraditional uses of PLCs, such as in the home and in medical equipment, haved exploded in the 1990s and will increase as we enter the new millennium. A person knowledgeable in relay logic systems can master the major PLC functions in a few hours, These functions might include coils, contacts, timers and counters. The same is true for a person with a digital logic background. For persons unfamiliar with ladder diagrams or digital principles, howere, the learning process takes more time. A person knowledgeable in relay logic can master advanced PLC functions in a few days with proper instruction. Company schools and operating manuals are very helpful in mastering these advanced functions. Advanced functions in order of learning might include sequence/drum controller, register bit use, and more functions. Following are 8 major advantages of using a programmable controller. ① Flexibility. In the past, each different electronically controlled production machine required own controller。 15 machines might require 15 different controllers. Now it is possible to use just one model of a PLC to run any one of the 15 machines. ② Implementing Change and Correcting Errors. With a wired relaytype panel, any program alterations require time for rewriting of panels and devices. When a PLC program circuit or sequence design change is made, the PLC program can be changed from a keyboard sequence in a metter of minutes. No rewiring is required for a PLCcontrolled system. ③ Large quantities of contacts. The PLC has a large number of contacts for each coil available in its that a panelwired relay has four contacts and all are in use when a design change requiring three more contacts is made. Time would have to be taken to procure and install a new relay or relay contact block. Using a PLC, howere, only three more contacts would be typed in. the three contact would be automatically available in the PLC. Indeed, a hundred contacts can be used from one relayif sufficient puter memory is available. ④ Lower cost. Increased technology makes it possible to condense more functions into smaller and less expensive packages. Now you can purchase a PLC with numerous relays, timers and counters, a sequencer, and other function for a few hundred dollars. ⑤ Pilot Running. A PLC programmed circuit can be evaluated in the office or lab. The program can be typed in, tested, observed, and modified if needed, saving valuable factory time. In contrast, conventional relay systems have been tested on the factory floor, which can be very time consuming. ⑥ Visual Observation. A PLC circuit’s operation can be seen during operation directly on a CRT screen. The operation or misoperation of a circuit can be observed as it happens. Logic paths light up on the screen as they are energized. Troubleshooting can be done more quickly during visual observation. In advanced PLC systems, an operator message can be programmed for each possible malfunction. In advanced PLC systems, an operator message can be programmed for each possible malfunction. The malfunction description appears on the screen when the m
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