The STD function block implements a user-defined state machine in a module. A state machine describes the possible states, and the transitions between those states, that can occur in a system. The combination of STD and SEQ blocks provide a sequencing capability similar to DeltaV Sequential Function Charts (SFC). STD blocks associate transitions with system states. SEQ blocks associate system states with actions.
State machines may be described by state transition diagrams. For example, a burner management system could be defined by the following diagram of the allowed transitions (arrows) between system states (circles).
Configure the number of states and transitions using the block's extensible parameter capability. The DESC_INx parameter defines the transition names and a named set defines the state names. The block's MATRIX parameter describes the state diagram (the association of states and input transitions).
The STD block does not support modes or alarm detection.
The following diagram shows the internal components of the STD function block.
