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"Future Applications of Simulators in Process Control," Review Copy, March 21, 1997
Future applications of simulators for process control will be driven by advancing capabilities in simulation
technology. Much of this advancing capability is the direct benefactor of advancing computing
technology. However, some advances have been pioneered for the art of simulation itself. Future
applications of simiulatorsin process control will see activities with high return on investment in areas such
as concurrent engineering, hardware-in-the-loop controller testing, process fault detection, and internet-
retrievable simulation models and tools.
In the past, custom real-time computers had to be developed from the ground up for demanding simulation
applications. Today, because of rapid growth in computational speed, available microprocessor
technology can be built upon for simulation uses. In some cases, this technology is making once only
theoretical applications a reality.
- Computing Technology --
The National Science Foundation is sponsoring a grant to implement asynchronous updating in real-time
simulators. The updating is not restricted to integer multiples of the base update rate. The proposed
technique, under development by Applied Dynamics International, uses an intelligent input/output (1/O)
processor card to predict outputs and update the outputs more frequently than the update rate from the
simulation processor executing the model. When the actual output is received from the simulation
processor, the intelligent I/O board will correct its output and use that information for its next prediction.
The new technique will allow off-loading of the simulation processor to larger time steps, thus making it
possible to process a more complex model. It will also allow variable-step-size integration algorithms in
real-time simulators, and the simulation-processor can be unburdenedlto deaLwith interrpts and other -
asynchronous events. In the past, real-time simulators have been restricted to fixed-size integration steps,
and could not perform much asynchronous processing.
Verv High Speed Simulation.
At the Redstone Arsenal in Huntsville. Alabama, it is finally becoming possible to perform digital,
hardware-in-the-loop simulations of the most computational demanding military- and space-related
systems. In the past, the fastest portions of these systems could only be simulated using analog systems
because the computational load exceeded existing technology. Bench-marking reports of new systems
tested there indicate that simulation frame-times are on the verge of breaking below the 10 ps level for
models with significant complexity. Digital simulation is preferred over analog simulation because digital
systems are more repeatable over time. Analog systems are subject to parameter drift and errors due to
temperature effects and component tolerances. Digital systems are more easily reconfigured by simply
changing software as compared to patch panels or hardware redesign required by analog systems.
Advances in network technology are making it possible to link computers together to share data at
increasing speeds. This enables multiple computers to work in parallel to simulate more complex systems.
It also enables more convenient connections between a simulator and a controller when performing
hardware-in-the-loop testing. Three types of network interfacing applicable to simulation will be reviewed.
A bus adapter or shared memory, as shown in Fig. 11, is an interface that connects two computer buses at
the physical layer. Typically, a block of memory from one bus is mapped to a block of memory on the
other bus. The two systems continue to operate independently and asynchronously, communicating by
data transfer through common memory. Dual port RAM enables the interface to appear as local memory to
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Ruppel, F. & Wysor, W. Future applications of simulators in process control, article, March 21, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc694908/m1/3/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.