System Design Course

The classical problems with system software logic are:

1. "Bugs," usually the result of insufficient specifications (analysis) and design.

2. Poor understandability and therefore, poor maintainability, usually the result of inferior design and documentation.  Just as quality cannot be inspected into manufactured goods like cars (or candy), reliability and maintainability cannot feasibly be tested into software.  The only feasible approach is to use disciplined methods from the very start.  Engineering programmers must have a "print" to work from, just as builders, electricians, plumbers, etc. do.

Classically there are two steps before implementation - Analysis and Design.  Analysis (functional specification) is the detailed description of the requirements of the system. Analysis specifies WHAT the system is to do, not HOW.  It is the critical link between the end customer and those providing the system.  Design is the infrastructure (frame, skeleton) for the logic or the code.

English language descriptions make poor analysis documents because of ambiguity and redundancy.  Methodologies that are structured, precise, and graphical are necessary.  The methodologies taught in the course are Sequential Function Charts (SFCs), and Yourdon methodology.

SFCs work best at describing sequential control functions, e.g. turn on Valve A, when 100Kg of syrup has been added, turn off Valve A and start mixer, etc.  The basic SFC section presents the SFC methodology, including all the rules for steps and transitions, leveling, etc. and reinforces these methods with exercises.  The advanced SFC section shows how complex, real-world processes can be tackled by using a "top down" hierarchical approach and/or by breaking the process up into smaller, inter-dependent pieces.

State Transition Diagrams (STDs) are a subset of SFCs that have been in use in North America for a longer period of time.  A chapter on STDs is included in the student book and optionally covered during the training sessions.

Yourdon methodology works best at describing systems (or parts of systems) that are very data processing intensive or algorithmic in nature, e.g. a self-tuning, adaptive control scheme to regulate the percentage of various components in a continuous blend.  The Yourdon section presents the tools of the methodology, including data flow diagrams (DFDs), mini-specs, and data dictionaries, along with student exercises.

The course moves from describing analysis methodologies to describing design tools – once we have an analysis for WHAT it is we want the system to do, we use design to bring discipline to the process of HOW it is done.  The design section focuses on several methodologies for rendering SFCs (and DFDs) in PLC logic.

Finally, the course examines project management.  This section focuses on the impact analysis and design efforts have on project schedules (loads more effort "up front" - but pays great dividends later), and how management "buy-in" will be required for this to be successful.

Who should attend?

This course has been tailored to the needs of those persons involved in managing, developing or implementing functional specifications for sequencing projects.  Although special emphasis is paid to PLC based implementations, the techniques discussed in the class apply to all implementation platforms when implementing sequencing applications.  The covered tools apply very well in scenarios in which specifications must be clearly understood amongst multiple members of a project team, or to help guarantee the correct interpretation of customer specifications when projects are performed by other departments or outside vendors.

This course has been very well received by groups of electrical and mechanical technical maintenance and engineering personnel.  In each case the participants left with high praise for the important concepts that were presented, and the need for improvement in most organizations in the area of analysis and specification.

The course material is delivered at a very fast pace in order to condense the information into a 3-day seminar.  There are many real-world automation examples and exercises to reinforce the use of the tools presented in the class.  The class involves a great deal of interaction between students as the numerous exercises are executed and presented to the class.

Course Customization

The course can be modified in a number of ways to meet the specific needs of the audience.  For example, the Yourdon-DeMarco section can be omitted to allowing addition time for students to complete exercises, or PLC implementation discussions can be omitted when instructing mechanical maintenance or management staff.  Additionally, customer specific examples and exercises may be developed in order to help the class see the applicability in their own plants, etc.

Integrated Process Automation & Control Technologies