Each component that is developed over the span of the project may vary according to the type of simulator that you require. A tieback simulator, for instance, does not incorporate a detailed process model, but instead uses simple control loops to simulate the process. For our full scope simulators, in which the process model and control system solution are site specific, the development process requires a combined effort between your simulator support team and our engineers.
The Process Model
The process model is the heart of the simulator! In a high fidelity simulator, it accurately emulates the physical process. For example, in a typical power plant 30-35 major systems must be modeled. These include such systems as the furnace, boiler, steam turbine, electrical switchyard, and auxiliary cooling systems. Each of these systems is made up of components such as pumps, valves, pipes, heat exchangers, motors, etc. Through the use of DYNSIM Power, SimSci-Esscor's process modeling tool, the process model is parameterized or developed. Simulation objects are adapted to match the features of the site's components to produce a realtime dynamic representation of the unit.
The Control System Representation
The process model stimulates the vendor's control software. The control system representation accurately simulates the calculations that take place in the vendor's actual control systems. These systems often include a Distributed Control System (DCS), Programmable Logic Controllers (PLCs), and hardwired relay logic. For a DCS, the best approach is to use a "virtual stimulation" product, such as FSIM Plus, to simulate the control calculations because the actual control system code is running in the simulation workstation. This provides an accurate simulation of these calculations.
The Input/Output Model
Once the process model and control system representation components are in place, there must be a way to link them together. At the actual site this is done with I/O cards and terminal strips. The control system sends signals to the actuators in the process. The actuators move in response to the signals. This results in modified process values, which are registered by the transmitters. These transmitter values are then sent back to the control system to close the loop. The I/O model serves the analogous purpose in the simulator. It consists of a cross-reference database, which links a mathematical variable in the process model (representing either a transmitter output value or an actuator input value) to the corresponding I/O point in the control system representation. The cross-reference database thus provides the closed loop between the process model and the control system representation.
The Operator Interface
With the three models discussed above we have an operational, controllable simulation. We now need an interface for the operation of the simulation. This is analogous to the control room at the site. The best choice for the simulator's operator interface depends on the type of interface at the site. For a DCS-controlled site, it is preferable to use the actual DCS hardware as the operator interface. This is what our FSIM Plus product does. For hard panel instruments, such as switches and strip charts, it is more efficient to graphically emulate them.
Since the operator interface is the only part of the simulator that the trainee will ever directly touch, it is important to have the utmost in fidelity.
The Instructor Station
The Instructor Station (I/S) is the control center of the simulator. The I/S allows access to the simulator's special features, which do not exist at the actual site. These include the ability to:
- Freeze and resume execution of the process model and control system representation
- Save and restore model states for future retrieval
- Execute the model faster or slower than realtime
- Introduce single malfunctions or groups of malfunctions
The I/S interface also lets the instructor monitor the progress of the training session with lists and trends of process and control system variables. Reports can be generated for use in operator qualification and scoring.
The High Speed Networks
The final components of the simulator are the high-speed networks, which link all the pieces together. The networks are the Nodebus (control system highway) and the Ethernet (simulator highway). In most cases the process model and the control system representation will both be located on the Master workstation. However, they can also be distributed across the simulator highway, as is the case when we integrate third party modeling packages into our simulators. The Instructor Station can be local (on the Master workstation) or remotely located on the simulator highway. The operator interface is connected to the Master workstation via the control system highway. All hard panel emulation workstations are located on the simulator highway.