Food Engineering

S88-Aware Phase Logic Control

March 27, 2003
The ISA S88 international standard is usually associated with batch-type processes. However, Foxboro has been successful in using object-oriented S88 models and terminology (Control Modules, Phases, Units, etc.) for sequential phase logic control in selected continuous-type processes, such as spray dryers. Here, frequent product changes and the necessary process start ups and shut downs must be handled orderly and efficiently. At Universal Flavors, each product change also requires a CIP cycle, which adds additional sequencing requirements.

"Foxboro's S88 approach and phase sequencing software makes the system easier to use and more bulletproof by forcing operators to perform a sequenced start up," says Norman Voigt, process manager, who oversees process control for Universal Flavors. "I especially like the way their solution maps very smoothly over the S88 model.

Control Modules receive their commands from the S88.01 Phases, which are isolated from the complexities of starting the control loop. The S88.01 Batch Executive starts phases according to a pre-defined recipe, which is changeable only through programming. However, the path through the recipe can be modified based on process conditions and operator input.