Sequential State Chart (SSC) is a sequence language which is useful for the description of procedures in industrial automation technology. At the same time, we can also use SSCs as an additional tool for project planning in engineering. Due to its intuitive syntax, SSCs can be applied without a deeper knowledge of the Automata Theory.

  Exemplary Sequential Function Chart with 3 different states Copyright: © PLT Exemplary Sequential Function Chart with 3 different states

SSC is based on the concept of a state machine which allows a description of sequences with the help of states and transitions. States may include actions that are executed once the state is activated. Actions can be the setting of a variable value or the execution of a function block or another SSC. Only one state can ever be active within an SSC. The activation of the subsequent step and thus, the deactivation of the current step are realized with the help of transitions. A transition that follows an active step switches once the transition conditions are fulfilled.

The states and transitions are embedded in an ‘execution frame’. This frame functions as an interface with the remaining control- and description structure and supports modularization and clear structuring. The interface of ‘execution frames’ is organized via inputs and outputs similar to the interface of function blocks.