The RE 3304 is RTK's analog process controller purpose-built for boiler feed water level regulation and steam flow rate control in industrial steam plants. It uses a 3-point stepping output to drive electric actuators (e.g., RTK Bauer ST 5100 series) for feed water valve positioning, with bumpless manual/automatic transfer to prevent level shocks during operator intervention. Digital variants (3304-8010) offer the same control algorithm with digital configuration.

How does the 3-point stepping control work?

The controller compares the 4–20 mA process value (water level, steam flow, or pressure) against the 0–100% setpoint. When deviation exceeds the adjustable sensitivity band (1–10%), the controller pulses either the "open" or "close" relay output to the electric actuator — each pulse incrementally repositioning the valve. PI or PID action modulates the pulse frequency and duration based on proportional band (Xp, 10–100%) and integral time. Fixed potentiometer feedback (200–1000 Ω) from the actuator provides valve position confirmation, enabling the controller to limit travel between adjustable upper and lower limit switches for alarm and safety interlock activation on extreme level deviations.

What additional boiler control features are available?

An optional trend connection monitors the rate of water level change, preventing low-water boiler shutdown during sudden load shedding — a common trip scenario when steam demand drops abruptly and feed water inflow lags. Optional three-component control integrates boiler water level, valve lift position, steam flow rate, and feed water flow rate for high-precision drum level management in multi-boiler plants. Disturbance and auxiliary control variable inputs allow cascading with upstream pressure or temperature loops. The switching dead zone (dx) should be set as wide as plant conditions allow to protect relay contacts and actuator motors from excessive cycling.