【正文】 are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLC read limit switches, analog process variables (such as temperature and pressure), and the positions of plex positioning systems. Some even use machine vision. On the actuator side, P L C operates electric motors, pneumatic or hydraulic cylinders, magic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a puter work that plugs into the PLC. P L C was invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers, and drum sequencers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the rewiring of hardwired control panels when production models changed. Many of the earliest PLC expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLC used a form of instruction list programming, based on a stackbased logic solver. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and working. The data handling, storage, processing power and munication capabilities of some modern PLC are approximately equivalent to desktop puters. PLClike programming bined with remote I/O hardware, allow a generalpurpose desktop puter to overlap some PLC in certain applications. Under the IEC 611313 standard, PLC can be programmed using standardsbased programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. 6039。s in last century, because of American car industry need to carry on largescale technique reformation and equipments to renew, from traditionally control equip to carry on a control after the electric appliances, not only the physical volume be huge, breakdown rate, gentle bad, ineffective live, consume ability, and adjust to try difficulty, the credibility is also year American . pany puts forward using conceive of new generation controller, consider from the customer39。 The life span is short and the credibility be bad。 Design a manufacturing a period long, procedure modification timeconsuming。s in last century, although the small scaled calculator has been gradually perfect and apply realm is also continuously extending, the small scaled calculator used for switch control system, obviously exist the circumstance of Malaysia pull a small car again, this is because the characteristics of small scaled calculator decide: The plait distance woven distance plications, requested to have higher level personnel and operate a personnel。 Function excess, the machine resources can not well make use of。 Use the solid I/ O electric circuit to examine the signal of button and limit switch, carry out organization by the control electrical engineering and the other for an exportation. The PLC system that