Process & Instrumentation Diagram (P&ID)

Selection of Controlled Variables

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Guideline 1.

All variables that are not self-regulating must be controlled.

Guideline 2.

Choose output variables that must be kept within equipment and operating constraints (e.g., temperatures, pressures, and compositions).

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Guideline 3.

Select output variables that are a direct measure of product quality (e.g., composition, refractive index) or that strongly affect it (e.g., temperature or pressure).

Guideline 4.

Choose output variables that seriously interact with other controlled variables.

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Guideline 5.

Choose output variables that have favorable dynamic and static characteristics.

Guideline 6.

Select inputs that have large effects on controlled variables.

Guideline 7.

Choose inputs that rapidly affect the controlled variables.

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