Software provides insight to process dynamics

As part of any control system project there is a need to accurately define requirements of the problem. Part of this effort for many processes extends beyond simply knowing the I/O requirements and the interlock functions to knowing timing and other dynamic constraints. In these systems, process-timing control is as important as the interlocks and may be the more complex control problem.

09/01/1999


As part of any control system project there is a need to accurately define requirements of the problem. Part of this effort for many processes extends beyond simply knowing the I/O requirements and the interlock functions to knowing timing and other dynamic constraints. In these systems, process-timing control is as important as the interlocks and may be the more complex control problem. To effectively understand the nature of the timing functions that must be controlled, the process must be modeled. Modeling includes timing charts, process scheduling, and dynamic modeling.

SimCad Professional from CreateASoft Inc. (Naperville, Ill.) is a software product with the capability to provide dynamic process modeling. Originally designed to model business operations, it also can model process and manufacturing operations. It features a graphical system that animates during simulation to provide the user a real-time "feel" for the modeled process.

The key to successful use of SimCad is establishment of the proper view of the graphical elements. These elements or "items" must be viewed as process operations, not process locations. For example, if a mixer is identified, time dynamics of the mixing process needs to be modeled. The other key concept of this package is an "object." In this case, because objects are the products of a given process, the final object of a bread bakery would be wrapped loafs of bread.

To use SimCad Professional, the following steps are required:

  • Create the model. This step defines the process functions that must occur. In a bakery, for example, they could be mix, bake, and package. This step also includes definition of the links among processes. SimCad includes a standard library of icons for the process images, and users can develop their own as standard bitmap files.

  • Define the objects. This step creates counters to track material movement through the process and forms the basis of the analytical effort.

  • Run the simulation. The software provides animation to indicate operations as well as a complete analysis package with both report and chart as its output.

  • Adjust model properties and repeat simulation until desired results are obtained. This includes use of the built-in process system failure feature to replicate upset conditions.

Use of SimCad's functions can be learned quickly. However, users need to be aware of two shortcomings at the start. Toolbar icon identification is inconsistent. Some icons identify at the mouse arrow, others identify at the bottom of the screen. Still others need to be pointed at and right clicked to see the description.

Additionally, the manual layout and indexing capabilities of the software make it difficult to find some topics. However, availability of on-line help functions helps to offset this difficulty.

Despite these minor obstacles, SimCad's analysis package can help users easily understand complicated system dynamics and the consequence of system upsets. Once these functions are understood, implementation of control functions for time sequence management and upset response become more manageable. This review was based upon version 3.1b of SimCad Professional.

For more information on SimCad Professional, visit www.controleng.com/freeinfo .


Author Information

Contributing Editor, Tracy J. Coates P.E. is a consulting engineer at PCE Engineering, Johnson City, Tenn.




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