Level Electrodes (Limiters) - SPECTORmodul | Gestra

GESTRA SPECTORmodul – Level Electrode Limiters

The GESTRA SPECTORmodul series comprises level limiting devices for steam boilers and pressurized hot water systems. The range includes low-level electrodes NRG 16-50 / 17-50 / 19-50 / 111-50 with electronic switch NRS 1-50, and high-level electrodes NRG 16-51 / 17-51 / 19-51 / 111-51 with NRS 1-51.

Operating Principle

Measurement is based on the conductivity of boiler water. At low level, the electrode rod is exposed, causing the NRS 1-50 to open the safety circuit of the heating system. At high level, the rod is immersed, allowing the NRS 1-51 to interrupt water supply. The switching point is determined by the electrode rod length.

Technical Data

• Electrode pressure classes: PN40, PN63, PN160, PN320
• Indicative low-level limits: 32 bar/238°C, 60 bar/275°C, 100 bar/311°C, 183 bar/357°C
• Connection: G¾ A ISO 228-1 or G1 A (NRG 111)
• Low-level rod lengths: 500–3000 mm
• Electrode protection: IP65
• Ambient temperature: up to 70°C

NRS Electronic Switch

The NRS 1-50 operates at 24 VDC or optionally 100–240 VAC, with power consumption 7 VA. Safety contacts rated 6 A / 250 VAC. Response delay 3 s. Standby input for blowdown monitoring via SRL 6-50. Sensitivity selectable for water conductivity: 0.5–1000 μS/cm or 10–10000 μS/cm.

Safety, Installation, and Standards

Combinations NRG 1…-50 / NRS 1-50 and NRG 1…-51 / NRS 1-51 are classified up to SIL 3 (IEC 61508) with 1oo2 architecture and self-diagnostics. For external level pots, regular blowdown is required; connections ≥40 mm (steam) and ≥100 mm (water) are considered internal installation. Not suitable for explosive atmospheres.

Applications and Use Cases

• Steam and hot water boilers (industrial/process/HVAC)
• Feedwater tanks, condensate receivers
• Suitable for water and steam media
• Used in safety interlocks, pump control, and overfill protection