This paper proposes the example expansion which enables development of large scale control systems without knowledge of real-time computing. In the example expansion, real-time system engineers familiar with programming for real-time computing develop a small example for maintaining the timing consistency. Since the example is small, its development and modification are easy. The example is expanded according to requirements specified by control engineers who have expertise in the regulation of a specific plant. Since formal rules and tools expand the example, a mechanism for maintaining the timing consistency is correctly transferred to a target system. The example expansion allows the two kinds of engineers to concentrate on their own work. A control system for a steel mill plant has been developed using this method, and the system has been developed 2.7 times faster than the time taken with a conventional method.