Impact of Communication Timeouts on Meeting Functional Requirements for IEC 61131-3 Distributed Control Systems

The control software is frequently used in various systems that perform important and responsible tasks in industry. During its development, it is crucial to ensure that the solution is created in a way consistent with assumptions and meets all functional requirements. One of important steps consists of testing particular software units, separated from the rest of system, using the off-line simulator. However, test results can be different in case of a fully-connected system when external factors, such as communication issues, should be also taken into account. In this paper, the authors present a concept of specification and execution of system tests, using the dedicated test definition language, named CPTest+. It has been extended by the additional ASSERT_COM instruction, which performs an assertion that is able to detect problems related to external factors, including communication. To enable automatic and systematic testing, the dedicated metric has been proposed. It takes into account the current link status and archived results to calculate the probability that the test case has failed due to communication problems.