Flowserve NRS 1-51 - Manual (Page 4)

4
Application
Usage for the intended purpose
The level switch NRS -5 is designed for different electrical conductivities of the boiler water and for
connecting one level electrode.
See section Schematic representations of arrangements on page 6.
When the water level exceeds the MAX limit, the level electrode enters the liquid and an alarm is
triggered in the level switch. This switchpoint is determined by the length of the electrode rod
(level electrode NRG ...-5, NRG ...-).
After the de-energizing delay has elapsed, both output contacts of the level switch will open the control
circuit, e. g. for the feedwater supply. If the deactivation of the feedwater supply is interlocked in the
external control circuit, the lockout can only de deactivated when the level electrode is exposed 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 autmatic self-testing routine monitors the safety functions of the level switch. In the event of a
malfunction the control circuit opens instantaneously and switches off e. g. the feedwater supply.
Alarm and malfunction messages are indicated by LEDs, and the signal output is instantaneously
energized.
An alarm can be simulated by pressing the test button.
Function
The level switch NRS -5 is used in conjunction with level electrodes NRG ...-.. as high level alarm in
steam boilers and (pressurised) hot-water plants.
A high level alarm prevents the water level from exceeding the preset max. water level (HW) and for this
purpose switches off e. g. the feedwater supply.
Depending on the specified directives or standards, the level switch NRS -5 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 6-5 NRG 7-5 NRG 9-5
VdTÜV Bulletin “Wasserstand 00”
(= Water Level 00)
NRG 6-5
NRG 6-
NRG 7-5
NRG 7-
NRG 9-5
NRG 9-
Note
n
A high level alarm prevents the water level from exceeding the preset max. liquid
level (HW). For this purpose it can, for instance, interrupt the feedwater supply. If the
interruption of the feedwater supply endangers the heating surfaces in the feedwater
preheater (economizer), the heating must be switched off, too.