6
Design
NRS 16-12, NRG 17-12, NRG 19-12
Mechanical connection: Screwed ¾", ISO 228-
Electrical connection: Four-pole connector/terminal box made from aluminium (optional)
Explanatory Notes
– continued –
Function
The high water-level limiter comprises a level electrode type NRG ...-2 and a level switch type NRS
-8. The level electrode NRG ...-2 consists of a pressure-tight measuring electrode. The electrode is
insulated with a plastic sleeve.
The high water-level limiter 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 not immersed in boiler water and no high level alarm is given. A high level alarm will only be
raised if the electrode tip is submerged for more than 3 seconds. A high 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 the water level in the
gauge glass. The equipment combination NRG ...-2 and NRS -8 provides fail safe protection against
a first fault in accordance with TRD 604.
System components
NRS 1-8
Level switch
NRS 1-8
. Two channel level limiter (redundancy) with periodic self-checking routine to
EN 5056-.
