Did you know that Goldilocks was an automation engineer? True story!
After that whole bear business, Goldilocks grew up, enrolled in her state’s university, and graduated with a degree in electrical and computer engineering. She’s been working in the industry for a few years now.
One day, not so long ago, she was designing a flexible ISA-88 batching system. She was at the step where determining what the phases would be for her units of operation was needed. She surveyed the big white board in front of her. Across the top, in big blue letters, was written, “A phase is an independent, self-contained processing action.”
She shifted her eyes to the column on the right side of the board. In this column were phases with descriptions like: Add all ingredients, control motors, and maintain product. “Hmm,” she thought, “Those phases don’t seem independent or self-contained. They are too big.”
She looked over to the column on the left. In this column were descriptions like: Control valve, control pump, and read tank temperature. Goldilocks considered for a moment and said, “Those phases aren’t processing actions. They are too small.”
Finally, she looked over to the column in the middle, with phase descriptions like: Control agitation, tank heating, single ingredient addition, and wait for temperature. “Ah,” she said, “those phases are just right.”
And so, she used the middle column as her basis for design and developed a well-balanced flexible batching system that increased the customer’s operational efficiency, improved product quality, and saved money over the life of the system.
The moral of the story:
Developing phases is all about balance. Make them too big and complicated and you lose the flexible part of the flexible batching system. Make them too small and your recipes become large and unwieldy. Consider the high-level steps that are required to make a product, those steps are good starting points for your phases:
· If some operation is always going to include a handful of devices, then that phase should probably include all of those relevant devices.
· If you can foresee all the steps required to make Product A, and making Product B excludes some steps, you should consider breaking out those steps as separate phases.
This way they can be easily removed rather than having to write two separate but similar phases to account for the difference.
You don’t want a phase to do only one thing. And you don’t want it to do everything. The sweet spot is somewhere in between. Then your phases will be just right!
Nicholas Imfeld is a principal engineer at Avanceon, a certified member of the Control System Integrators Association (CSIA). For more information about Avanceon, visit its profile on the CSIA Industrial Automation Exchange.