What is reset windup and how is it prevented?

Reset (integral) windup occurs when controller output saturates (fully open/closed) but error persists, causing integral term to keep accumulating. When error reverses, excessive integral accumulation causes large overshoot before integral unwinds. Prevention methods: external reset feedback (integral tracks actual valve position), conditional integration (stop integrating when output saturated), and velocity algorithm (inherently handles saturation). Modern DCS systems include anti-windup automatically. Critical for batch processes, startup/shutdown, and override control where saturation is common.