The GESTRA NRR 2-50 and NRR 2-51 are water level limit controllers from the SPECTORmodule family, designed for steam boilers, hot water installations, condensate tanks, and feedwater tanks. Both process level-dependent signals from GESTRA NRG electrodes or NRGT transmitters and provide PI (Proportional-Integral) control with configurable MIN/MAX alarm contacts.

What is the difference between the NRR 2-50 and NRR 2-51?

The two models differ in how they drive the control valve:

Choose the NRR 2-50 for motorized electric valves requiring step control; choose the NRR 2-51 for pneumatic or I/P-positioned valves requiring a continuous analog control signal. Both models share the same DIN rail housing, 24 VDC supply, and PI control algorithm.

What sensors are compatible?

Both controllers accept GESTRA NRG 21-.. / NRG 26-21 capacitance level electrodes (3-pole with screen) or NRGT 26-.. / NRGT 26-1 / NRGT 26-2 level transmitters with 4–20 mA output (2-pole with shield). A 4-pole code switch on the front panel selects the input type. Up to three NRS/NRR 2-5x units can be connected in parallel for electrode inputs or in series for transmitter inputs, supporting redundant level monitoring in safety-critical boiler applications.

How is PI control configured?

The controller continuously displays the actual water level as a percentage (0–100% of measuring range) on a 4-digit green LED display. Adjustable PI parameters — proportional band (Pb), integral action time (ti), and setpoint (SP) — are configured via a rotary knob with integrated push-button. The control action can be set for fill control or drain/discharge control. On malfunction, MIN and MAX alarms trigger automatically and the system attempts a restart. An alarm off-delay of 3 seconds prevents nuisance trips from transient level fluctuations.