Guardian SCC 25, Manual

Page: 45 / 79

Page 45
GUARDIAN SCC-40 Issue (Auto VI) & V3.6t 07/12/00
LOW STAGE OR HIGH STAGE DETECTS SAFETY TRIPS
Any safety trip immediately de-energises the motor contactor by hard wiring
which removes the motor running signal from both controllers.
If the safety trip is on the low stage then the low stage controller indicates the trip
condition and flashes the 'Tripped' lamp, whilst the high stage controller flashes
its 'Tripped' lamp and indicates 'nnot' ( motor running fail) since it cannot detect
any other trip.
If the safety trip is on the high stage then the high stage controller indicates the
trip condition and flashes the 'Tripped' lamp, whilst the low stage controller
flashes its 'Tripped' lamp and indicates 'nnot' ( motor running fail) since it cannot
detect any other trip.
LOW STAGE DETECTS TRIPS
If the low stage detects a high or low trip limit condition then the Stop-slave
signal is given to the high stage and the low stage motor relay output is
immediately removed which de-energises the motor contactor. The high stage
shuts down in a normal stopping sequence even though the motor contactor has
already been de-energised.
The low stage indicates the trip condition and lights its 'Tripped' lamp.
HIGH STAGE DETECTS TRIPS
If the high stage detects a trip condition condition then the STOP_MASTER
signal is given to the low stage and the high stage motor relay output is
immediately removed which de-energises the motor contactor.
The low stage shuts down in a normal stopping sequence.
The high stage indicates the trip condition and lights its 'Tripped' lamp.
HIGH STAGE STOP REQUEST
When a high stage Manual Stop request is given, then the high stage
compressor goes into its stopping sequence and issues a Stop-slave signal to
the low stage master prior to removing the high stage motor relay signal which
de-energises the motor contactor. The low stage goes into its stopping
sequence, lowers its slide to At_Minimum and then removes the low stage motor
relay signal (the motor contactor is probably already de-energised).
Both high stage and low stage compressors run their oil pumps until the
appropriate slides are At_minimum and both controllers display 'Waiting' followed
by 'Ready'.
REMOTE OPERATION
When all three low stages are selected to REMOTE mode then one low stage
controller takes over as best compressor and does suction pressure control and
communications to all other low stage controllers as described in the
section :- CONTROL OPERATION
High stage controllers are started and stopped as required by their associated
low stage. Guardian SCC-40 Remote mode communications currently supports a
maximum of 4 controllers.
ECONOMISER VALVES
On HS-U and LS-U controllers the economiser valve is open whilst the motor
relay output is present.