Towards Contract Based Assertions in IEC 61499 Applications

The IEC 61499 standard addresses the topic of function blocks for industrial process measurement and control systems. It defines a generic model for distributed control systems and offers more flexibility but requires severe discipline from the designer, since arbitrary event driven execution models can be difficult to analyze and debug. Presuming a composable function block model, contracts allow formally specifying assumptions and guarantees on the ports of a function block. This work proposes an initial concept for integrating behavioral assumptions and guarantees into function blocks in IEC 61499. Monitors implementing these contracts can observe the function block’s behavior during its execution. They check the adherence to the contract either on a local node or after distributing the function blocks on a network of controllers. In this work, we have implemented our concept based on 4diac, an open-source IEC 61499 compatible framework. We illustrate and evaluate our concept with a simple water level control system