Advanced Control Strategies & Calibration
Cascade, ratio, feedforward, split-range control, P&ID documentation, ISA symbols, calibration procedures, SIL/SIS, and analytical instruments.
- Explain cascade, ratio, and feedforward control strategies
- Describe split-range control and advanced strategies
- Interpret P&ID symbols and ISA tag numbering
- Outline calibration procedures, SIS concepts, and analytical instruments
Lección 1
Cascade, Ratio & Feedforward Control
Cascade Control
In a cascade control system, two controllers are connected in series. The output of the primary (master) controller becomes the setpoint of the secondary (slave) controller. The secondary loop responds to fast disturbances before they affect the primary variable.
For example, in a heat exchanger, the primary controller measures outlet temperature and sets the setpoint for the secondary flow controller on the heating medium. Flow disturbances are corrected by the fast secondary loop before the temperature changes significantly.
Ratio Control
Ratio control maintains a fixed ratio between two flow rates. One flow is the "wild" (uncontrolled) flow and the other is the "controlled" flow. The ratio station multiplies the wild flow by the desired ratio to generate the setpoint for the controlled flow.
Feedforward Control
Feedforward control measures the disturbance directly and applies a correction before the disturbance affects the process variable. Unlike feedback control which reacts after the fact, feedforward anticipates changes. It is often combined with feedback (cascade) for the best results.
Cascade vs Feedforward
Cascade uses two feedback controllers in series. Feedforward measures the disturbance directly and acts before the process is affected. Both improve control over single-loop feedback.
In cascade control, the primary controller output is the setpoint of the secondary controller. Feedforward measures disturbances directly and acts before they affect the process variable.