Flowserve NRS1-8 - Manual (Page 5)

5
Explanatory Notes
– continued –
Function
The level switch NRS -8 is a two-channel unit provided with an automatic self-checking circuitry in
accordance with DIN VDE 06 prEN 5056 (directives for protection circuits). The self-checking is
effected periodically. The test includes the checking of the cable between electrode and level switch and
of the self-checking circuitry (redundancy). The output relays are not influenced by the internal tests.
In addition to this self-checking routine, the level switch can also be tested manually by pushing the
button “Test ”, simulating a defect in the electrode. The test switch “Test /Inspection” is provided for
checking the function of the checking circuitry.
As the circuit of the relay contacts of the level switch is normally closed, alarm will also be signalled in
the event of a mains failure.
The level switch can signal the following three operating conditions:
n
Normal operation (correct level)
n
Alarm (high level)
n
Alarm (malfunction in level switch or electrode)
The green LED indicates power supply. The high level or malfunction alarms are indicated by two red
LEDs. The failure of one channel (loss of redundancy) is signalled by the illumination of a single red LED.
The combination of electrode NRG 6-, NRG 7-, NRG 9- and level switch NRS -8 provides
fail-safe protection against a first fault, i. e. the system will still continue to provide the safety function
even after the occurrence of a first fault.
System components
NRG 16-12
Level electrode NRG 16-12, PN 40
NRG 17-12
Level electrode NRG 17-12, PN 63
NRG 19-12
Level electrode NRG 19-12, PN 60
Design
NRS 1-8
Plug-in unit in plastic case for installation in control cabinets. The terminals in the case are accessible
after loosening two screws and unplugging the unit from its base.
To avoid confusion with other plug-in units of the GESTRA range, inserts are fitted in the bases so that
only the correct unit may be plugged into each base.
The plug-in unit may be snapped onto a 35 mm supporting rail or screwed into position on a mounting
panel.