Industrial Control systems can be divided into two categories, those that are designed for general-purpose control functions and are fully programmable by the end userwww.cechina.cn, and those designed for a special purpose, such as controlling a milling machine or an injection molding system.
        In the first categorywww.cechina.cn, one typically finds PLCs and general-purpose industrial computers. The second category uses dedicated controllers with built-in support for special functions, such as closed-loop motion control. Both systems benefit from multitasking—the ability to perform more than one function at the same time—but dedicated controllers place special requirements on the operating system's coordination of concurrent tasks.
        Where time-critical functions are involved, such as the control and coordination of multiple axes of motionCONTROL ENGINEERING China版权所有, the operating system must guarantee that time critical signals from motion tracking sensors are not missed by the control application's critical threads. An operating system like Microsoft Windows cannot provide sufficient response guarantees to host such an application, because it is optimized to provide services to a variety of general-purpose tasks, such as interaction with human operatorsCONTROL ENGINEERING China版权所有, network interfaces, database enginesCONTROL ENGINEERING China版权所有, etc.
        This general-purpose aim does not bode well for the timing requirements of an industrial control application, which requires a real-time operating system to guarantee the coordination of time-critical functions. But the highly specialized nature of a real-time operating system is also a severe limitation.
        A general-purpose operating system like Microsoft Windows has many third-party tools available to shorten the time required to implement operator interface screens, access databases, and com