Flowserve NRG 111-11 - Manual (Page 5)

5
Explanatory Notes
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Description
The level electrode NRG 111-11 detects the min. liquid level (low level alarm) in a steam boiler. The
operation of the electrode is based on the conducitivity measuring principle using the electrical
conductivity of water for signalling one liquid level:
■ Low level alarm (MIN alarm)
The NRG 111-11 is designed for use in conjunction with level switch NRS 1-7 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 1 and sheet 2
(24h/72h operation) as well as EN 12952 and 12953.
The electrical equipment meets the requirements of the Regulations on Protection Circuits DIN VDE
0116 (prEN 501565-1).
Function
Design
The water level limiter comprises the level electrode type NRG 111-11 and GESTRA level switch NRS
1-7. The level electrode NRG 111-11 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 signalling 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 cavities between the body, tube and stud. 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 111-11 and
NRS 1-7 provides fail safe protection against a first fault in accordance with TRD 604.
If the internal ceramic insulation breaks steam and hot water may escape through the lateral relief
vent of the electrode stem.
NRG 111-11:
Level electrode with screwed connection 1" BSP, ISO 228-1. Fig. 1
System Components
NRS 1-7
Level switch NRS 1-7, 0.5 µS version. The limiter features a two channel circuit (redundancy) and an
automatic periodic self-checking routine in accordance with DIN VDE 0116 (prEN 50156-1).