Inferential Control Control Using a Single Secondary Measurement

Objectives The concept of inferential control(IFC). Structure and analysis of control using one secondary measurement. Inferential control versus classical control strategies. Application of IFC to a distillation column control

Applications

Generic Inferential Control Problem

Classical Approaches: Feedback Control of Secondary Variable

Composition control using temperature

Classical Approaches: Cascade Control

Classical Approaches: Feedforward Control

Classical Approaches: Feedback Using an Output Estimator

2 DOF Internal Model Control

Inferential Control Structure

Disturbance Estimator

Controller Design

IFC Structure

Example

Step Responses

Combining Feedback with IFC

Summary  Inferential Control is used when a measurement of the primary variable is not available.  Inferential control is similar to a cascade control strategy.  IFC can suppress disturbances detected by the secondary measurement.  IFC can lead to bias if model errors are present  When ever possible combine IFC with direct feedback control of primary variable even if it is infrequently measured.