Automated Verification of Function Block Based Industrial Control Systems

Abstract IEC 61131-3, the world-wide standard for industrial control programming, is increasingly being used in embadded control applications. The standard supports the concept of reusable “software ICs” through the concept of function blocks. can be hierarchically grouped and horizontally “wired” to Complex control loops are typically built from elementary components taken from domain-specific libraries. Code inspection and testing are the two predominant quality assurance techniques in practice, today. For highly dependable control applications, however, these techniques are not sufficient, in general. This paper suggests to augment testing with compositional, theorem-prover supported verification. The approach is based on a representation of IEC 61131-3 function blocks in higher-order logic. The verification task is separated into the a priori verification of library components and a separate proof of individual application programs. The latter relies on proven properties of the library components used. We sketch the semantic embedding of three most used languages of the IEC standard and illustrate our verification approach with a simple example. We conclude with a wish list for a verification tool that is usable by application and licensing engineers.