Simulation of a Steam-Boiler

In this paper, we describe the implementation and usage of a simulation with graphical visualization for a steam-boiler [Abri94]. The simulation imitates the behaviour of the steam-boiler and can be controlled using a simple ASCII protocol. It reacts to defined commands and sends information about its state every five seconds. Furthermore, we describe the options available, the protocol which functions as an interface between the simulation and the controller, and how one can simulate component failures within the boiler. We give information about the simulation and how to install it. 1. Goal and Motivation The aim of the steam-boiler case study is to examine various formal methods in relation to the steam-boiler specification problem. In the case study, different solutions to the steam-boiler specification problem are compared. One aspect of this comparison is to investigate the ability of a method to create or to develop an executable program. Our aim is to provide a graphical visualization of a steam-boiler simulation, which can be used to show the validity of a control program. Using this simulation, one connects a program to it and tests the program. To limit the effort needed for connecting the simulation and the program, we have chosen a simple ASCII protocol to interface the simulation. 2. Architecture and Behaviour of the Simulation The simulation imitates the behaviour of the steam-boiler. In Figure 1, a view of the running simulation is shown. On the left side, there are the four pumps with four pump controllers which determine the water influx. On the right side, the boiler with a valve, a scale, the water level display (the black label) and the steam measurement device are shown. Every five seconds, the simulation sends messages about the status of its devices (physical units). Devices are defined as: pumps, pump controllers, water level display, and the steam measurement device. According to the task description, after sending messages, the simulation has to stop and must continue to imitate the behaviour of the steam-boiler, only when it receives the commands from the program. In a realistic situation in a plant, this synchronous assumption cannot be satisfied. Therefore, we decided not to implement a synchronous simulation. Instead, our simulation keeps running after sending the status messages and executes the commands, as soon as they are received. A delay may occur due to the time needed for transmission.