Flowserve NRG16-41 - Manual (Page 6)

6
Explanatory Notes
continued
System components
NRS 1-41
Digital switching controller for high-level limiter NRG ...-4
Functions: High-level alarm (M
ax
)
Data exchange: CAN bus to DIN ISO 898 using CANopen protocol.
URB 1, URB 2
Control terminal and display unit
Functions: Parameterization and visual display (LCD)
Data exchange: CAN bus to DIN ISO 898 using CANopen protocol.
Design
NRG 16-41, NRG 17-41, NRG 19-41:
Screwed ¾", EN ISO 8-. Fig. 2, Fig. 3
Function
The conductivity of the liquid is used to signal the liquid level. Some liquids are conductive, which
means that they allow an electric current to flow through them. For the safe functioning of this device a
minimum conductivity of the liquid to be measured is required.
The conductivity measurement method can detect two conditions: electrode rod submerged or
exposed, meaning switchpoint reached (or exceeded) or not yet reached. Before installation, the length
of the electrode rod must be cut to the required switching level, e. g. for “Pump
off
” or “Control valve
closed
” or, in case of economiser and air heaters that are installed close to the steam-generating unit
and exposed to a risk, “Firing/Burner
off
”.
An additional electrode fully integrated in the system automatically monitors the electrical resistance
path between earth and measuring electrode. As soon as the actual value falls below the admissible
resistance value the protection circuit is interrupted and cuts off the pump or heat supply to the boiler.
At regular intervals the level electrode NRG ...-4 sends a data telegram to the switching controller
NRS -4. The data are transferred via a CAN bus to DIN ISO 898 using the CANopen protocol.