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GESTRA NRS1-50 100-240V AC LEVEL SWITCH
GESTRA NRS1-50 100-240V AC LEVEL SWITCH

GESTRA NRS1-50 100-240V AC LEVEL SWITCH

The GESTRA NRS 1-50 level switch plays a vital role in plant safety and operational reliability. It does not operate independently; it is always used in conjunction with one or two GESTRA level electrodes based on the conductivity principle (e.g., NRG 16-50, NRG 19-11, NRG 111-50). Its main task is to prevent the water level from falling below a defined minimum, thus protecting the boiler and plant from damage.

Key areas of application include:

  • Steam Boilers (Plant and Boiler Safety):
    • Low Water Level Limiter: This is its most common application. When a dangerously low water level occurs in the boiler water, it automatically shuts off the burner (heating system) to prevent boiler overheating, material damage, and potentially severe accidents. This is a mandatory safety function for unattended boiler operations (24/72 hours) according to applicable safety standards (TRD 604, EN 12952, EN 12953).
    • High Water Level Alarm: Depending on the electrode configuration, it can detect excessive water levels, preventing overflow or water carry-over into the steam line.
  • Pressurized Hot Water Installations: Provides similar safety functions as a low water level protection.
  • Condensate and Feedwater Tanks: Used to monitor minimum or maximum water levels in these tanks and control associated pumps or valves.
  • Functional Safety Applications (SIL): When used in combination with GESTRA's self-monitoring NRG series electrodes, it can achieve a functional safety level of up to SIL 3 according to IEC 61508. This makes it ideal for applications requiring high reliability.
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GESTRA NRS 1-50 is an electronic level switch that processes signals from the connected level electrode(s) and controls relay outputs accordingly. It fundamentally operates on the conductivity principle: when the electrode tip becomes exposed from the water (i.e., becomes dry), this condition is detected by the switch, and a low water level alarm is triggered.

Key Features:

  • Self-Monitoring: The NRS 1-50 continuously monitors not only the water level but also the status of the connected electrode(s) and its own internal circuitry. In the event of contamination, leakage in the electrode insulation, or an electrical connection fault, it immediately triggers a fault signal (alarm) and opens the safety circuit (shuts off heating). This feature significantly increases the fault-safety (fail-safe) of the system.
  • Adjustable Sensitivity: It offers adjustable response sensitivity based on the electrical conductivity of the boiler water (e.g., > 0.5 µS/cm or > 10 µS/cm).
  • Delay Times: The response delay can be adjusted (e.g., 3 seconds for low water level, 15 seconds for marine applications), which prevents nuisance alarms from short-term agitation or level fluctuations.
  • Output Contacts: It features two potential-free normally open (NO) contacts for shutting down the heating system (safety circuit). It also has instantaneous signal outputs for external signaling.
  • Test Function: An integrated test button allows for simulation of an alarm condition to test the safe operation of the system.
  • LED Indicators: Provides LED indicators for operating status, alarm, and fault messages.
  • Wide Supply Voltage: The 100-240V AC input voltage makes it suitable for use in various electrical grids worldwide. A 24V DC supply option is also available.

The NRS 1-50 is a compact unit designed for DIN rail mounting and is typically installed within a control panel.

  • Model: NRS 1-50
  • Type: Level Switch (Used with external electrodes)
  • Operating Principle: Evaluation of signals from external conductivity electrodes.
  • Supply Voltage: 100-240 V AC (+10 / -15 %), 47-63 Hz, 0.2 A, or 24 V DC (+/- 20 %), 0.3 A.
  • Power Consumption: Approx. 7 VA.
  • Response Sensitivity (Electrical conductivity of water at 25 °C):

    • 0.5 ... < 1000 µS/cm

    • 10 ... < 10000 µS/cm (selectable)

  • Number of Connectable Electrodes: One or two GESTRA conductivity electrodes (e.g., NRG 16-50, NRG 17-50, NRG 19-50, NRG 19-11, NRG 111-50, NRG 16-36).
  • Safety Circuit Output: 2 potential-free normally open (NO) contacts, 6 A 250 V AC / 30 V DC (cos φ = 1).
  • Response Delay (for Safety Circuit): 3 seconds (standard), 15 seconds for marine applications.
  • Signal Output: 1 or 2 potential-free outputs for instantaneous external signaling (24 V DC, max. 100 mA).
  • Stand-by Input: For monitoring the purging and bypass time of level pots outside the boiler (controlled by GESTRA SRL 6-50 logic unit).
  • Indicators: LEDs for operating status, alarm, and fault diagnostics. Test button.
  • Ambient Temperature: -10 °C to +55 °C during operation.
  • Protection Class:
    • Housing: IP 40 (according to EN 60529)
    • Terminal strip: IP 20 (according to EN 60529)
  • Mounting: Clip-on mounting on supporting rail TH 35, EN 60715.
  • Approvals: EC type approved according to PED (Pressure Equipment Directive) 2014/68/EU, EN 12952/EN 12953, functional safety up to SIL 3 according to IEC 61508 (with compatible electrodes), VdTÜV Bulletin "Wasserstand 100", UL, FM, and approvals from various marine classification societies.