Advanced Process Control - Split Range Control

Flashcards reviewing the principles, applications, and tuning methods of split range control loops, including duplex control strategies and block diagrams.

Duplex Control

A control strategy where two independent control elements share a common input signal for the operation of separate final control elements, influencing the controlled variable using two manipulated variables.

Split Range Control Strategy

A duplex control strategy where each final control element (FCE) uses a specific portion of the control signal; each manipulated variable uses only a portion of the control signal.

Full Range Control Strategy

A duplex control strategy where both final control elements use the full range of the control signal.

Advantage of Duplex Control

Simpler to implement and requires only one controller instead of two, compared to a standard control strategy.

Temperature Control (Duplex Control Application)

Uses a cooling manipulated variable and a heating manipulated variable.

Energy Economizing (Duplex Control Application)

Uses final control elements for cooling/heating and bypassing to optimize fluid flow between process units.

Neutralization (Duplex Control Application)

Uses acidic and caustic manipulated variables to neutralize waste effluent.

Dilution Control (Duplex Control Application)

Uses two control valves (manipulated variables) for coarse and fine adjustments to paper pulp consistency.

Excess Gas Flaring (Duplex Control Application)

Controls gas pressure using throttling valves; one valve captures gas, the other flares excess gas safely.

Duplex Split Range Control Block Diagram

Shows each FCE using a portion of the controller's output signal; Controller Output (CO) affects different control valves based on its range (0-50% or 50-100%).

Duplex Full Range Control Block Diagram

Shows both FCEs using the full range of the controller's output signal simultaneously.

Tuning Split Range Control Systems

If static gain, dead time, and time constant are similar, tune as a linear control loop; otherwise, use adaptive gain or detuning methods due to differing transfer functions.

Detuning

Tune the fastest acting loop as a linear control loop, accepting a sluggish response when controlling the slower acting process.

Adaptive Gain Control Strategy

Uses the controller's output to switch tuning parameters when the CO crosses 50%, optimizing control in each range.

Preventing Dead Zone Cycling

Calibrate control valves to overlap in their operating range to eliminate dead zones.

Tuning Full Range Control Systems

Duplex full range control systems with only one transfer function should be tuned as standard feedback control loops.

Tuning Full Range Control Systems with Two Controllers

Tune the controller directly affecting the controlled variable first (with the other in manual), then tune the second controller (with the first in automatic) using a slower, non-oscillatory method.