When it comes time to define the requirements for a control system, control engineers often find many options available to assist with this function.

This is in part the result of the varied types of documentation needed for different phases of the design and implementation process, as well as the range of automation applications. Control system designers must first examine the application(s) in question and the company's business culture to determine the best tool or tools to use for design documentation.

Two common areas requiring design documentation are state/transition and data flow. In state/transition, the design of process steps, limits, and interlocks must be captured. For data flow, users and their data requirements must be determined. In both areas, text description, graphical representation, or a mix of each may be chosen to convey design details to all involved parties.

A software package that gives control system designers a range of graphical options is System Architect from Popkin Software (New York, N.Y.). This package is primarily marketed towards business application development but the functionality included offers control system designers graphical means of conveying system design.

Within System Architect, many types of graphical representations can be used for process control modeling. These include:

• IDEFO
• Gane&Sarson Data Flow
• Ward&Mellor Data Flow
• Yourdon
• State Transition

Because input and output signals (digital or analog) are, in fact, simply data to a control program, data flow diagrams are easily used to represent data interrelations and movement though a system. Data movement includes storage and to other computers for analysis. Additionally, movement of data values between control functions and the requirements for operator input/intervention are also easily depicted. Therefore, the designer can illustrate a system from field inputs though the control processor, its relationships with the human-machine-interface and the HMI-to-operator interaction.

"Child" diagrams help System Architecture simplify—an important capability. A process box within diagrams represents a summary of actions, and a related diagram shows details under that summary. A child diagram can be created by any diagram type and is not limited by the type that was the "parent."

In creating these diagrams, different formats offer boxes for processes that may be used for physical or computer operations, arrows for material movement, and connecting arrows for data movement. One problem with the package, however, is that it can be difficult to route arrows (either material or data) the way desired. While origin and termination are easily set, the software does not always cooperate on the route across the page.

It should be noted that the functionality of this package goes beyond that addressed in this review. Here the focus has been on the ability to graphically depict logic sequences and data flows. System Architect also can compile to object code from these completed graphical structures, if the associated databases are defined and completed.

System Architect runs under Microsoft Windows 95/98 and NT including as a network application. This review is based on System Architect 2001 software package, version 7.1.12.

For more information about System Architect, visit www.controleng.com/freeinfo.