An automation style is a standardized methodology for creating and implementing control system modules across a facility. Think of it as your "playbook" — ensuring consistency in how automation systems are structured, programmed, and deployed. Two primary styles are recommended:
A methodology where the system's behavior is determined by its current process state and the inputs it receives. The controller maintains knowledge of the current operational state and makes control decisions based on that state information.
A process state represents a specific condition or mode of operation. The system can only be in one process state at a time. Transitions between states are triggered by specific input conditions, timers, or external signals.
Key advantage: Allows operators to run the entire selected process in automatic mode with minimal manual intervention. Covers the complete operational cycle from start-up through normal operation to shutdown and back.
When to use SBC:
Industrial example: A pump control system with states "Stopped," "Starting," "Running," and "Fault." Transitions occur based on commands, sensor confirmations, and fault detection.
A programming approach where processes are controlled through predefined steps executing in a specific order. Essentially converts written Standard Operating Procedures (SOPs) into automated control logic. Each step waits for specific input conditions before advancing.
When to use SqBC:
Implementation: Typically uses Sequential Function Charts (SFCs) in PLC/DCS programming. SFCs provide visual representation of process flow with clear transitions between steps.
| Characteristic | State-Based Control | Sequence-Based Control |
|---|---|---|
| Active steps | Only one step active at a time | Multiple steps can be active simultaneously |
| Execution model | State machine with transitions | Sequential execution of predefined steps |
| Coverage | Complete operational cycle | Specific procedure execution path |
| Operator mode | Full automatic with minimal intervention | Step-by-step execution with checkpoints |
| Best for | Continuous processes with distinct operating modes | Batch-like procedures, SOP conversion |
Style selection should consider:
Consistency in automation style across a facility reduces operator learning time, reduces opportunity for errors, and reduces engineering costs for development and maintenance.
Both styles use steps and transitions as building blocks:
Transitions can be Normal (sequential), Forward (skipping ahead to a later step), or Backward (looping back to retry a step). This provides flexibility for exception handling and optimization paths.
Regardless of style, implementation modules must: