FYI. 第一代技术： Contact-Dependent Control ·Hard-wired connections with protection, relays, and time relays ·Centrally located control boxes Programmable Logic Controllers (PLCs) ·Increased flexibility due to freely programmed connections ·Central PLC in a centrally located control box 第二代技术： Networked PLCs ·First step towards distributed intelligence: Many small PLCs networked together over a common bus system ·Smaller control boxes, placed closer to the point of action Decentralized Periphery ·Input and output devices (sensors, actuators) installed on site and connected via a bus system with the centralized PLC ·Reduced wiring of the input and output ports ·Continued centralized automation over the PLC, because sensors and actuators are not intelligent 第三代技术 Decentralized Automation (LONWORKS) ·Current state of development ·Sensors and actuators are provided with their own intelligence and exchange information with one another directly ·No need for a “center” ·Information processing on site ·Minimal wiring ·Maximal flexibility for expansion 详见：《LonWorks Installation Handbook》（英文版） lonworks@gongkong.com

PLC一般体现厂家专有系统，不能使不同厂家PLC产品互操作，不是开放互操作的系统。