可编程逻辑控制器plc外文翻译-plc设计(编辑修改稿)

可编程逻辑控制器plc外文翻译-plc设计(编辑修改稿)内容摘要：

difications are needed only if additional, changed, or relocated input/output devices are involved. All programmable controllers consist of the basic functional blocks shown in Figure . 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 es the I/O bloke. 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, motor starters, DC and AD drivers, solenoids, and printers as outputs . An adaptive control system is one whose parameters are automatically adjusted to pensate for corresponding variations in the properties of the process. The system is。