關(guān)于plc的畢業(yè)設(shè)計(jì)外文及翻譯-plc設(shè)計(jì)(已修改)
2025-06-01 16:02 本頁面
【正文】 PLCs Past, Present and Future Everyone knows there39。s only one constant in the technology world, and that39。s change. This is especially evident in the evolution of Programmable Logic Controllers (PLC) and their varied applications. From their introduction more than 30 years ago, PLCs have bee the cornerstone of hundreds of thousands of control systems in a wide range of industries. At heart, the PLC is an industrialized puter programmed with highly specialized languages, and it continues to benefit from technological advances in the puter and information technology worlds. The most prominent of which is miniaturization and munications. The Shrinking PLC When the PLC was first introduced, its size was a major improvement relative to the hundreds of hardwired relays and timers it replaced. A typical unit housing a CPU and I/O was roughly the size of a 19 television set. Through the 1980s and early 1990s, modular PLCs continued to shrink in footprint while increasing in capabilities and performance (see Diagram 1 for typical modular PLC configuration). In recent years, smaller PLCs have been introduced in the nano and micro classes that offer features previously found only in larger PLCs. This has made specifying a larger PLC just for additional features or performance, and not increased I/O count, unnecessary, as even those in the nano class are capable of Ether munication, motion control, onboard PID with autotune, remote connectivity and more. PLCs are also now wellequipped to replace standalone process controllers in many applications, due to their ability to perform functions of motion control, data acquisition, RTU (remote telemetry unit) and even some integrated HMI (human machine interface) functions. Previously, these functions often required their own purposebuilt controllers and software, plus a separate PLC for the discrete control and interlocking. The Great Communicator Possibly the most significant change in recent years lies in the munications arena. In the 1970s Modicon introduction of Modbus munications protocol allowed PLCs to municate over standard cabling. This translates to an ability to place PLCs in closer proximity to real world devices and municate back to other system controls in a main panel. In the past 30 years we have seen literally hundreds of proprietary and standard protocols developed, each with their own unique 39。s PLCs have to be data pilers and information gateways. They have to interface with bar code scanners and printers, as well as temperature and analog sensors. They need multiple protocol support to be able to connect with other devices
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