Comment

May 2009

Documentation standard rouses plant productivity

By Alex Habib

Control software documentation has been an ongoing problem for engineering, operations, and support practitioners of industrial control and plant-wide automation systems. The industry needs to be aware of a methodology of documentation that can be a natural part of the engineering process—one that expands or modifies easily as designs improve or field modifications develop.

One such document, ANSI/ISA-5.06.01 standard, Functional Requirements Documentation for Control Software Applications, has been out for over a year, but its important users (automation and process engineers in chemical, petrochemical, pharmaceutical, food and beverage batch, and continuous process industries) understand the advantages of having such a methodology available to them.

The standard establishes functional requirement specifications for control software documentation that covers the classes of industrial automation equipment and systems consisting of distributed control systems, programmable controllers, and industrial process computers. It provides techniques for documenting control system software, as well as a basis for validation of run-time application software after it is developed and tested to ensure it meets the initial requirement specification.

The standard addresses this need starting from a single-product continuous manufacturing plant to a multi-product multi-recipe batch plant. To document the functional requirements of today’s control software packages, control engineers must use a combination of ladder diagrams, Boolean logic diagrams, flow charts, time sequence diagrams, block diagrams, and written process operating procedures. And to top it off, they must convert the ladder and Boolean logic diagrams to the higher-level process control system (PCS) programming languages.

Generating and maintaining all of these documents can be time-consuming and expensive. What would help is a simple, universal system of documentation that control system engineers, plant operators, and system manufacturers can easily develop and interpret as they are designing and testing control software.

ISA5.06.01 applies to several batch control plants, the most recent of which is a multi-recipe, multi-product specialty chemicals plant.

This concept of software documentation, which involves mainly the sequence control logic function, has proven to be an effective way of transferring the process technology and operational know-how of an existing pilot scale operation to a new, fully automated, large-scale production plant.

Defining requirements

The standard is especially helpful in bulk chemical, fermentation, biotechnology, specialty, and fine chemicals industries in that it helps engineers define requirements and test the control system and validate it, which is especially critical in pharmaceutical processes.

By starting with a solid and clear definition of a requirement, when the system is ready to be tested, the standard makes it easier to revisit process intent to assure it met the requirement—that nothing in the process or batch has changed.

If someone added an ingredient or made an error in writing code, users can validate the process through the use of the standard, and through the different phases of development, ensure they end up with same thing they started with.

Programming languages are specialized, and only certain people know how to read and write them. So it is crucial to have a document that anyone can review and critique and check. That is what ISA5.06.01 does; it defines the requirement, and it is very specific and detailed so anyone can develop, generate, and review.

Batch sequence matrix

The Batch Sequence Matrix in ISA5.06.01 helps users define, develop, and test the control software of the plants’ PCSs. Benefits include savings in the number of man hours required for software design, as well as timely control system validation, commissioning, and plant start-up.

Traditionally, the most complicated and difficult to define, the sequence matrix, addresses the problem of defining a requirement. If an engineer wants to automate the process in which the sequence is manual, he must first describe it to the programmer. So he uses the standard to describe the requirements in simple terms. The person who understands the process knows how the batch reactor or distillation column works, but he wants to translate this knowledge to a programmer. So bridging the communication gap is the whole idea with the standard.

ABOUT THE AUTHOR

Alex Habib, P.E., is a principal automation consultant in Old Bridge, N.J., a senior member of ISA, president of the Central NJ Section of ISA, VP-elect of ISA’s Management Division, and chairman of the SP5.6 Committee on Software Documentation Standard for Control Systems.