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无线系统的控制回路挑战
本文讨论了用无线传感器网络实现控制环路的挑战。它着眼于不同的封闭和开放控制回路架构和能够支持它们的无线网络协议的延迟要求。
虽然可以使用Wi-Fi与嵌入式模块如Microchip的mrf24wb0mb，最近的协议如isa100a和WirelessHART™目的无线网络内提供集中的支持控制回路。设备如Atmel的at86rf231，恩智浦JN5148和Silicon Labs的em357已经支持IEEE802.15.4 Zigbee标准可以用来支持这些协议和严格控制回路定制版本。
不同于传统的控制系统，在传感器、执行器和集中控制器之间有专用的同轴电缆，采用无线通信的控制系统需要传感器和控制器共享用于通信的公共无线介质。当闭环控制系统使用公共通信系统实现时，网络的质量是整个系统性能的重要部分。许多系统中不重要的时间延迟可能成为实时闭环系统中的关键。
The problem is that tradiTIonal short-range wireless network standards such as IEEE 802.11 Wi-Fi and IEEE 802.15.4 ZigBee do not consider packets according to their delay deadlines and treat the packets all the same regardless of these requirements. This presents a major issue for a closed loop control system where the data from the sensors is used to control the actuators that influence the process. Delays in the data can lead to negaTIve reinforcement so that a process can run away rather than be kept within close limits.
This is different from an open loop system where the data is fed back to a central controller， analyzed with changes made in the order of seconds or even minutes. This is used for slowly changing processes or situaTIons where the process falls outside its limits and can easily be brought back or the process terminated.
