GESTRA NRS 1-50

ONE/TWO Electrodes Level Switch

Description

GESTRA NRS 1-50 Level Switch

GESTRA NRS 1-50 ONE/TWO Electrodes Level Switch
The GESTRA NRS 1-50 is a high-performance level switch controller designed to monitor and control water levels in steam boilers and pressurized vessels. Working in conjunction with one or two electrodes, it acts as a safety cut-out device to prevent low water conditions, thereby protecting boiler systems from potential damage or hazards.

Whether for industrial steam systems, HVAC boilers, or process steam applications, the NRS 1-50 ensures fail-safe operation, full compliance with EN standards, and reliable automation.

The level switch NRS 1-50 is used in conjunction with level electrodes NRG 1……. to limit the water level in steam boilers and (pressurised) hot-water plants.

Water level limiters switch off the heating when the water level falls below the set minimum level (low water).

Depending on the directives listed below the level switch NRS 1-50 can be used in combination with the following level electrodes:

Directive	Level electrode type
Functional safety accessory to IEC 61508 SIL 3	NRG 16-50, NRG 17-50 NRG 19-50, NRG 111-50
Functional safety accessory to VdTÜV Bulletin 100	NRG 16-50, NRG 17-50 NRG 19-50, NRG 111-50, NRG 16-36	NRG 16-11, NRG 17-11 NRG 19-11, NRG 111-11, NRG 16-36
Marine applications, e.g. DNV/LR Directives	NRG 16-50S, NRG 16-11S	NRG 16-38S, NRG 16-39S

Function

The level switch NRS 1-50 is designed for different electrical conductivities of the boiler water and for connecting one or two level electrodes.
When the water level falls below the low level the level electrodes are exposed and a low level alarm is triggered in the level switch. This switchpoint is determined by the length of the electrode tip.
After the de-energizing delay has elapsed, the two output contacts of the level switch will open the safety circuit for the heating. The switching-off of the heating is interlocked in the safety circuit and can only be deactivated when the level electrode enters the water again.
In addition, two signal outputs for external signalling devices close instantaneously.
An alarm will also be raised if a malfunction occurs in the level electrode and/or the electrical connection.
If the level electrode is installed in a level pot outside the boiler, make sure that the connecting lines are rinsed regularly.
During the rinsing process the water level cannot be measured in the level pot for 5 minutes. The level switch therefore bypasses the level electrode and monitors the rinsing and bypass time (standby input, controlled by the logic unit SRL 6-50).
If the connecting lines for steam ≥ 40 mm and water ≥ 100 mm, the installation is considered to be internal. In this case the rinsing processes do not have to be monitored.
An automatic self-testing routine monitors the safety functions in the level switch and the level electrode. In the event of a malfunction the safety circuit opens instantaneously and switches the heating off.
Alarm and errror messages are indicated by LEDs and an alarm can be simulated by pressing the test button

Technical Data

Supply voltage

24 VDC +/– 20 %, 0.3 A

100 – 240 VAC + 10/– 15 %, 47 – 63 Hz, 0.2 A (optional)

External fuse

M 0.5 A (semi-delay) Power consumption 7 VA

Sensitvity of response

(Electrical conductivity of water at 25 °C)

> 0.5 … < 1000 μS/cm or > 10 … < 10000 μS/cm

Electrical connection of level electrode

To connect the level electrodes please use:

For level switch NRS 1-50 with response sensitivity 10 μS: Screened multi-core control cable, conductor size 0.5 mm2, e.g. LiYCY 4 x 0.5 mm2, max. length 100 m.
For level switch NRS 1-50 with response sensitivity 5 μS: Double-screened multi-core low-capacitance data cable, min. conductor size 0.5 mm2, Li2YCY PiMF 2 x 2 x 0.5 mm2, max. length 30 m.

Stand-by input

2 volt-free inputs, 24 V DC, for monitoring the purging and bypass time. Max. bypass time: 5 minutes.

Wiring: control cable 2 x 0.5 mm2.

Safety circuit

2 volt-free make contacts,
6 A 250 V AC / 30 V DC cos ϕ = 1.
Delay of response: 3 seconds, 15 sec. for marine applications.
Provide inductive loads with RC combinations according to manufacturer‘s specification to ensure interference suppression.

Signal output

2 volt-free outputs for instantaneous external signalling, 24 V DC, max. 100 mA (semiconductor output).

Wiring: control cable 2 x 0.5 mm2.

Indicators and adjustors

buttons for test and diagnosis, 4 red/green LEDs for indicating the operating mode and alarm.
red LEDs for fault diagnosis, 2 two-pole code switches for setting the number of electrodes.

Housing

Housing material: base: polycarbonte, black; front: poly- carbonate, grey. Terminal strips separately detachable Fixing of housing: Mounting clip on supporting rail TH 35, EN 60715.