Flowserve NRS 1-50 For TWO Electrodes - Manual (Page 4)

4
Application
Usage for the intended purpose
The level switch NRS -50 is used in conjunction with level electrodes NRG ...-.. 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 specified directives or standards, the level switch NRS -50 is intended to be used in
combination with the following level electrodes:
Level electrode NRG 1...-..
PED Pressure
Equipment Directive
97/3/EC +
Functional Safety IEC
6508 SIL 3
NRG 6-50 NRG 7-50 NRG 9-50 NRG -50 NRG 6-36
VdTÜV Bulletin
“Wasserstand 00”
(= Water Level 00)
NRG 6-50
NRG 6-
NRG 7-50
NRG 7-
NRG 9-50
NRG 9-
NRG -50
NRG -
NRG 6-36
Marine applications
GL/LR Directives
NRG 6-50S NRG 6-S NRG 6-38S NRG 6-39S
Function
The level switch NRS -50 is designed for different electrical conductivities of the boiler water and for
connecting one or two level electrodes.
See section Schematic representations of arrangements on page 6.
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 rod
(level electrode NRG ...-50, NRG ...-, NRG 6-36).
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 external safety
circuit and can only be deactivated when the level electrode enters the water again.
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 an isolatable 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 ≥ 00 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
electrodes. 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 a signal output for each level electrode is
energized without delay.
An alarm can be simulated by pressing the test button.