Instead of modulating a valve continuously, you cycle a valve on/off. The ratio of on-time to off-time (duty cycle) determines the average energy input. Common for electric heaters in batch jacketed reactors.
The master engineer knows when to apply gain scheduling (batch) versus cascade control (continuous). But the foundation remains:
A disturbance is measured before it affects the PV. For example, measuring a change in inlet flow to a heat exchanger and pre-adjusting the steam valve. Combining feedback + feedforward is the gold standard for continuous processes.
