Control Engineering

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A Rose is a Rose by any other name, but Mode is used to describe all flowers, vegetables and other foods
November 18, 2007

The Make2Pack group continues to refine a way to discuss modes and how the term applies to the Control Components that make up the S88 Spectrum of control as used by the Make2Pack group. Our current thinking has evolved to two classes of “mode” for this effort. The scope of the Part 5 effort encompasses only the Equipment Phase Control through Equipment Basic Control, which is used to carry out a S88 Process Task Strategy, but it is important to understand how the Equipment and Recipe Procedural control elements relate to the Process Task Strategy Control Components.

The first class is how the internal activity of a single Control Component will behave and the algorithm’s relation to the outputs it directly manages. We are calling this the Mode of Action. Each Control Component will have a Mode of Action.

The second class is how multiple Control Components operate & interact together to carry out a more complex activity than is reasonable in a single control Component. We are calling this the Mode of Control. Each grouping of Control Components will have a Mode of Control that is descriptive of what that grouping is designed to accomplish.

Class 1:
The internal activity of any control component will generally have at least the two classic modes described by S88 of Automatic and Manual. In the example of a PID function block when in a mode of Automatic the PID algorithm will be directly managing the Output. When the PID function block is in Manual the algorithm is no longer managing the Output which is now managed by something outside of the function block, sometimes an operator through some form of Human Machine Interface (HMI). Two examples of an HMI are digital values on a graphic display and a physical rheostat on a panel. Other Control Components might also be able to manipulate the output through this method.

If the Control Component is sufficiently complex and capable of executing complex sequences or procedures and will be manipulation the inputs of other Control Components being able to manage the internal execution of the sequence or procedure becomes important. In this situation the S88 Procedural Modes of Automatic, Semi-Automatic and Manual.

It is possible for a Control Component to have more than one Mode that describes its behavior, these modes can complementary to one another and can be active at the same time. Besides Auto/Manual some other possible modes for Class 1 Control Components are: Simulation/Not-Simulation, Active/Inactive and any others that might be required. The Control Components themselves will generally manage this internal mode and might do so based upon the overall Mode of Control that this Control Component is part of.

Class 2:
When two or more Control Components are grouped together to carry out a function it is often beneficial to allow these grouping to be represented by the concept of a Mode that describes what it is that grouping is designed to accomplish at any given time. Modes such as: Cascade Control of PID loops, Operator Control for recovery from process upsets, and Maintenance Control for any unforeseen requirements. When considering larger groupings Modes such as Clean-Out, Sanitization, Production and others are often used. 

S88 Part 5 Spectrum of Control: From the left, the icons say Cell Procedural Control, Unit Procedural Control, Operation Procedural Control, Equipment Phase Control, Equipment Sequenced Control, and Equipment Basic Control.

Having a method to manage and coordinate the different possible modes for a Control Component grouping is a requirement and can be viewed as a separate Basic or Sequence Control Component that manages the group or groupings of other Control Components.

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Posted by David Chappell on November 18, 2007 | Comments (0)