Abstract
One of the main obstacle that prevents model checking from being widely used in industrial control systems is the complexity of building formal models out of PLC programs, especially when timing aspects need to be integrated. This paper brings an answer to this obstacle by proposing a methodology to model and verify timing aspects of PLC programs. Two approaches are proposed to allow the users to balance the trade-off between the complexity of the model, i.e. its number of states, and the set of specifications possible to be verified. A tool supporting the methodology which allows to produce models for different model checkers directly from PLC programs has been developed. Verification of timing aspects for real-life PLC programs are presented in this paper using NuSMV.
Highlights
CERN, the European Organization for Nuclear Research, relies on a large number of PLC (Programmable Logic Controller) applications to operate its different particle accelerators
This paper proposes two different approaches for modelling time and timers in PLC-based control systems
Experimental results applied to a real PLC program developed at CERN and an analysis of both approaches have been presented
Summary
CERN, the European Organization for Nuclear Research, relies on a large number of PLC (Programmable Logic Controller) applications to operate its different particle accelerators. The realistic approach represents the behaviour of timers and the internal representation of time in PLCs with high fidelity Such modelling allows to verify time-related properties to ensure that a given action will (or will not) be performed after or before a given delay (e.g. PLC output set to true 500 ms after a given input has been set to true). While this modelization is powerful in terms of expressivity, it may produce models that are too big to be handled by model checkers and leads to the second modelling approach. A tool implementing the two types of time modelization and generating formal models for NuSMV (Cimatti et al (2002)), BIP (Basu et al (2011)) and UPPAAL (Amnell et al (2001)) has been developed and applied to CERN’s control systems
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