資源目錄里展示的全都有，所見即所得。下載后全都有,請(qǐng)放心下載。原稿可自行編輯修改=【QQ：401339828 或11970985 有疑問可加】 Programmable Controllers In the 1960s, electromechanical devices were the order of the day as far as control was concerned. These devices, commonly know as relays, were being used by the thousands to control many sequential –type manufacturing processes and stand-alone machines. Many of these relays were in use in the transportation industry, more specifically, the automotive industry. These relays used hundreds of wires and their interconnections to affect a control solution. The performance of a relay was basically reliable-at least as a single device. But the common application for relay panels called for 300 to 500 or more relays, and the reliability and maintenance issues associated with supporting these panels became a very itself, the installed cost of the panel could be quite high. The total cost including purchased pars, wiring and installation labor, could range from $30-$50 per relay. To make matters worse, the constantly changing needs of a process called for recurring modifications of control panel. With relays, this was a costly prospect, as it was accomplished by a major rewiring effort on the panel. In costly prospect, as it was accomplished by a major rewiring effort on the panel. In addition, these changes were sometimes poorly documented, causing a second-shift maintenance nightmare months later. In high of this, it was not uncommon to discard an entire control panel in favor lf a new one with the appropriate components wired in a manner suited for the new process. Add to this the unpredictable, and potentially high, cost of maintaining these systems as on high-volume motor vehicle production lines, and it became clear that something was needed to improve the control process –to make it more reliable, easier to troubleshoot, and more adaptable to changing control needs. That something, in the late 1960s,was the first programmable controller. This first ”revolutionary” system was developed as a specific response to the needs of the major automotive manufacturers in the United States. These early controllers, or Programmable Logic Controllers(PLC),represented the first systems that(1) could be used on the factory floor, (2)could have there ”logic” change without extensive rewiring or component change, and(3)were easy to diagnose and repair when problems occurred. It is interesting to observe the progress that has been made in the past 15 years in the programmable controller area. The pioneer products of the late 1960s must have been confusing and frightening to a great number of people. For example, what happened to the hardwired and electromechanical devices that maintenance personnel were used to repairing with hand tools? They were replaced with “computers” disguised as electronics designed to replace relays. Even the programming tools were designed to appear as relay equivalent presentations. We have the opportunity now to examine the promise, in retrospect, what the programmable controller brought manufacturing？ All programmable controllers consist of the basic functional blocks shown in Figure 10.1.We will examine each block to understand the relationship to the control system. First we looked at the center, as it is the heart of the system .It consists of a microprocessor, logic memory for the storage of the actual control logic, storage or variable memory for use with data that will ordinarily change as a function of the control program execution, and a power supply to provide electrical power for the processor and memory .Next comes the I/O block. This function takes the control level signals for the CPU and converts them to voltage and current levels suitable for connection with factory grade sensors and actuators. The I/O type can range from digital, analog, or a variety of special purpose “smart” I/O which are dedicated to a certain application task. The programmer is normally used only to initially configure and program a system and is not required for the system to operate. It is also used in troubleshooting a system, and can prove to be a valuable tool in pinpointing the exact cause of a problem. The field devices shown here represent the various sensors and actuators connected to the I/O. These are the arms, legs, eyes, and ears of the system, including pushbuttons, limit switches, proximity switches, photosensors, thermocouples, position sensing devices, and bar code reader as input; and pilot light, display devices, and bar code reader as input; and pilot light, display devices, motor starters, DC and AC drivers, solenoids, and printers as outputs. 開關(guān) 傳感器 行程開關(guān) 模擬量 光電耦合 輸出端口 電機(jī)接觸器 電磁裝置 照明 輸出 中央處理器（CPU） 邏輯控制器 變量存儲(chǔ)器 動(dòng)力供應(yīng) 輸入端口 編程設(shè)備 輸入 圖1