Flowserve NRG 16-11 - Manual (Page 5)

5
Explanatory Notes
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Description
The level electrode NRG ...- detects the min. liquid level (low level alarm) in a steam boiler.
The operation of the electrode is based on the conductivity measuring principle using the electrical
conductivity of water for signaling one liquid level:
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Low level alarm
The NRG ...- is designed for use in conjunction with level switch NRS -7 as a self-monitoring low
level limiter with periodic self-checking (SMART) feature.
Application in steam and pressurised hot-water plants in accordance with TRD 604, sheet  and
sheet  (4 h/7 h operation) as well as EN 95 and EN 953.
The electrical equipment meets the requirements of the Regulations on Protection Circuits
DIN VDE 06 (prEN 5056).
Function
The water level limiter comprises a level electrode type NRG ...- and a level switch type NRS -7.
The level electrode NRG ...- consists of two concentrically arranged electrodes (measuring electrode
and compensating electrode) which are isolated from each other by special insulating seals.
The level limiter operation is based on the conductive measuring principle using the electrical
conductivity of water for signaling water level. During normal, trouble-free operation the level electrode
tip is immersed in boiler water and no low level alarm is given. A low level alarm will only be raised if
the electrode tip is exposed for more than 3 seconds. A low level alarm will also be activated if the
insulating seals placed between the electrodes and the body are no longer pressure tight, allowing
water to penetrate into the body. However in this instance the alarm is caused by a malfunction of the
electrode, and confirmation should always be done by checking if there is water in the gauge glass.
The equipment combination NRG ...- and NRG -7 provides fail safe protection against a first fault
in accordance with TRD 604.
Scope of supply
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NRG 17-11
 Level electrode NRG 7-, PN 63
 Joint ring 7 x 3, form D, DIN 7603, .430, bright-annealed
 Disk with set screw (measuring surface extension) – optional
 Retaining ring – optional
 Installation manual
NRG 19-11
 Level electrode NRG 9-, PN 60
 Joint ring 7 x 3, form D, DIN 7603, .430, bright-annealed
 Disk with set screw (measuring surface extension) – optional
 Retaining ring – optional
 Installation manual
System components
NRS 1-7
Level switch NRS 1-7. Two channel level limiter (redundancy) with periodic self-checking routine to
DIN VDE 06.