Industrial control systems (ICSs) present security risks related to their IT vulnerabilities. However, ICS systems have more constraints than IT systems represented by the interaction between cyber and physical systems. This interaction should be taken into consideration by the security solution. Intrusion detection systems give visibility of system branches and considered as one of the solutions to ensure the proper functioning. In this paper, we propose a rule generator for IDS. This rule generator takes a physical model and converts it into a syntax understandable by the IDS. This solves the difficulty of creating and maintaining handmade rules.