🔍 Key Concepts

• Triple-element (three-element) boiler feedwater control: what three variables are sensed and why this improves drum level control under changing load • Difference between proportional, reset (integral), and rate (derivative) actions in control systems • Why simple on/off (two-position) or single-mode control is usually not adequate for main propulsion boiler drum level on ships

💭 Think About

• Ask yourself: in a high‑pressure main propulsion boiler with rapidly changing steam demand, what kind of controller behavior is needed to prevent both slow drift and sudden level swings? • Think about what problems each control mode addresses: which one removes steady‑state error, which reacts to present error, and which anticipates rapid changes? • Which combination of modes would a designer choose for the most stable, precise control in a critical system like main propulsion feedwater, especially during rapid maneuvering or sea state changes?

✅ Before You Answer

• Identify what the three "elements" are in triple‑element control (hint: they are NOT the three control modes; they are three separate measurements). • Match each answer choice to the number of control modes it uses, and consider whether that matches the complexity implied by "triple element". • Eliminate any option that would allow large level overshoot or sluggish correction during rapid changes in steam flow, since that is unacceptable for main propulsion boilers.