18
2.4 SET-UP
Description
Once all the connections from the converter to the NSU are made, the NSU detects a
set of normally open or normally closed contacts connected at the connectors from J1 to
J13. After detecting the contacts, the NSU polls the converter and the associated switch
module in each chain position for a response. If both respond, the NSU Redundancy
Chain Status display will show the switch module position (ST or ON) and the NSU then
will consider the chain position active. If the NSU-Converter Serial link is disabled for a
chain position, communication with the converter is unnecessary. If a unit does not
respond to a poll a fault will be generated and the blinking characters will appear on the
Redundancy Chain Status display in that chain position. If the NSU cannot
communicate with the converter the upper numeric characters will blink, if the NSU
cannot communicate with the Switch Module the lower characters will blink. In the case
of the switch module, if communications has never been established with the switch
module in this position the lower characters will blink ”??”. Otherwise, the last known
switch position will be displayed and blink. An event will be entered into the Event Log
as well. If the system configuration does not require a serial connection between the
NSU and a converter, the NSU-Converter Serial Link should be disabled for that
position. It is important to note that disabling the NSU-Converter serial link will prevent
the NSU from becoming automatically updated with any operational changes to that unit
although fault status will still be sensed. Once all the converters and switch modules
have been connected to the NSU and been properly setup the NSU can be switched to
the AUTO redundancy mode where it will monitor the redundancy chain.
Converter failures are determined by detecting the state of the form-c redundancy switch
contacts that come from each converter. If a Primary converter faults, the NSU will
back-up the failing unit and generate Event log entries related to the failure. If a problem
occurs with a converter’s redundancy switch contacts, they open up or they become
shorted together (states other than a normally open or normally closed fault), the NSU
will treat that as a fault and back-up the affected position. If a converter stops
responding to NSU polling, the NSU will retain the last known operational parameters
and continue to protect the converter.
If a switch module for a given path stops responding to NSU polling or the switch
indicates a fault, a fault will be reported in the NSU. The NSU will continue to operate.