This white paper discusses the importance of control system integrity in the design and implementation of operator training systems.
One of the most important, yet overlooked, decisions in the development of an operator training system is the design of the off-line automation system. In many cases, the discussion around the simulation fidelity of the process models takes precedence over the discussion of the control system integrity or fidelity. This can lead the user into selecting and designing operator systems that might not meet the need of the plant operations.
If the purpose of the operator training system is to allow the operators to master the skills of using the control system to operate the plant, the selection of the off-line control system should be a high priority.
Training System Fidelity
Fidelity as it applies to simulation systems can be defined as the degree to which a system accurately reproduces the original. Specifically, an off-line automation system that provides high fidelity or integrity will support accurate or exact implementation of the following operator training system components, including:
- Operator graphics, faceplates, detail display, help screens
- Alarm strategies, priorities, timing, and operator acknowledgement and action response
- Control strategies including control module, equipment module, sequence and batch, and advanced control loops response
- Depending upon the role of operations at the plant, the off-line system may need to provide accurate and exact implementation of the following system components:
- Physical system management tools such as system explorers and diagnostic systems
- Digital bus IO based systems, especially systems using Foundation Fieldbus
Emulation, Stimulation, and Partial Stimulation
Many simulation companies and industry analysts have used the term stimulated, partial stimulation, and emulated for the methods in which the off-line control system is implemented.
Emulated Methods provide a simulation of the automation system consistent with the look and feel of the operating system. This is usually the method preferred by the simulation system vendor. It eliminates any system integration issues with the off-line automation system and allows complete control of the simulation environment. Instability issues associated with simulation speedup and slowdown are eliminated in emulated systems. However, emulated systems do not protect the integrity or fidelity of automation systems and do not support accurate implementation of the training system components listed above. Emulated systems should be avoided for operator training systems and should only be used for plant design modeling systems.
Stimulation Methods refer to the use of actual automation system components that accurately and exactly represent the key training system components listed above. Operator training systems should use Stimulated methods for best results.
Partial Stimulation Methods may use actual automation system components with some Emulation of lower complexity parts of the automation system like PLCs or safety systems. Partial Stimulation methods may be applied to operator training systems, however, careful decisions must be made about which parts of the system will be Stimulated and which are Emulated.
Maintaining Training System Integrity
Once the decision has been made to choose a Stimulation or Partial Stimulation method for the training system implementation, there are some additional requirements to consider.
Minimize or eliminate additions to the automation system application software. By not allowing additions, the user will minimize the effort required to merge updates from the operating system to the training system. Logic for simulating IO values or process responses should be in the process simulator alone. In addition, logic for operator training scenarios should be in the process simulator and not in the control system. It is acceptable to integrate the training system data at the operator station as long as no additions are made to the automation system application software.
Minimize or eliminate deletions to the automation system application software. It is a common practice for some simulation companies to remove elements that are not actively simulated from the automation system configuration. This practice is done to allow a narrow simulated IO scope for the convenience of the simulator. This reduces the realism of the operator experience when elements are missing or inoperable from the training system displays. In addition, by not allowing deletions the effort to merge updates from the operating system will be minimized.
Simulate all automation system IO signals. By having all control loops and signals simulated, the realism of the training environment is much greater. In order to keep simulation development costs under budget, the use of Selective Fidelity methods should be applied to the simulation development. Selective Fidelity describes the process of selectively applying low to high fidelity simulation dynamics to units operations based upon the operational and training needs. Simulator utilities should auto-generate the basic low fidelity simulation automatically from the automation system database.
Use only Non-Intrusive Simulation Interfaces. Non-intrusive simulation interfaces allow the control system to run in native, standard mode without modification to the configuration. Non-intrusive simulation interfaces are external to the automation system and interact with the IO level of the system without modifying the control system configuration.
The Business Results
By following the guidelines in this white paper, the user can expect an operator training system that is:
- More effective to train his operators on the safe and effective control of the plant.
- Easier to maintain and keep current with the production system.
- Capable of meeting the requirements of plant Operational Excellence Initiatives.