Tom Nolan, ProSys
This post examines the attributes of state based control and the value delivered to manufacturing from the initial design through the operating life of the facility by improving the effectiveness of operators. This is part 1 of a 5 part post and is an introduction to state based control.
Processes operate in a number of different states which range from down-time for maintenance to running in steady state and any normal or abnormal state in between. State based control uses the state or mode that the process is in to optimize the control of the process.
The result is a plant that performs better over the entire range of states for safety and asset utilization. The use of standardized established architecture can reduce the time and effort to implement the control system with improved performance.
Operational process knowledge is captured and leveraged in the design process. This keeps the knowledge of the best operator on the board at all times and reduces training demands. The knowledge, once captured, can also be leveraged through the corporation, improving the return on the initial investment. All of the operators on the board can manage the process at a higher level based on the experience and collective knowledge of everyone running the plant. The causes the plant to become smarter over time.
State based control is much more robust in the management of abnormal situations than monolithic control. State based control is designed to capitalize on knowing that what is normal in one state, is abnormal in another. State based control incorporates instrument justification and dynamic alarm rationalization into the design process. This reduces the initial cost to build and maintain, requiring only the instruments that are essential for a specific purpose, while eliminating I/O creep and the rework associated with it. It reduces start up time and alarm loading on operations during the critical commissioning of a new plant. This allows the plant to start up at the ISA 18.2 standards for alarm loading.
As far as safety is concerned, state based control goes beyond the typical safety instrumented systems design. It coordinates driving each operating unit to a predefined, appropriate, safe state that is beyond just a safety function. This safe state can be used for any number of different safety functions. Operators can quickly monitor that the systems have gone to the safe state and are performing correctly.