Guardian SCC 25, Manual

Page: 47 / 79

Page 47
GUARDIAN SCC-40 Issue (Auto VI) & V3.6t 07/12/00
AUTOMATIC STANDBY COMPRESSOR CHANGEOVER AFTER TRIP
IF auxiliary VI relay selection is Setup SySt = 'Stby' then VI-1 relay may be used
to switch a multi-pole relay which routes all microswitch and safety trip inputs
and control relay outputs to provide automatic compressor control changeover
after any trip.
The changeover sequence is as follows:-
Suction pressure higher than setpoint
VI-1 relay de-energised
compressor 1 input/outputs connected to SCC controller
compressor 1 automatically starts and runs
... some time later
compressor 1 trips - flashing trip lamp
delay after stop timer started
- trip data still displayed
when delay complete - automatically reset trip lamp
VI-1 relay energised
compressor 2 input/outputs connected to SCC controller
compressor 2 automatically starts and runs
... some time later
compressor 2 trips - flashing trip lamp
delay after stop timer started
when delay complete - automatically reset trip
VI-1 relay de-energised
compressor 1 input/outputs connected to SCC controller
compressor 1 automatically starts and runs
etc.
If more than 6 trips occur in a 24 hour period with security keyswitch not present
then the message 'CALL FRIG ENGINEER' is displayed and the system will not
reset until the security key is selected or the passcode entered.
MANUAL SELECTION
The VI-1 relay (Stby) can be forced to a particular compressor by using 'raise'
or 'lower' pushbuttons on VI selection in SetuP SySt as follows:-.
Use SetuP SySt noVI to de-energise the relay for compressor 1
or SetuP SySt Vi-1 to energise the relay for compressor 2
The automatic standby changeover feature is restored SetuP SySt Stby.