Fridgewatch 2100 Controller Mk4
Section 3
Publication 3-58
Issue 1.1 : 01/08
Page 27 of 152
When refrigeration is required, the master Fridgewatch 2100 Controller
always attempts to start its own compressor first. However, if the master
compressor is not available to start, for example, waiting on the starts per
hour timer to expire, but the slave compressor is available, this
compressor is started first.
When the slave compressor loads to maximum, the master compressor is
started as described in 5.5.2. Starting and Stopping the Slave
Compressor. Exactly the same starting, stopping and capacity control
criteria are used, except instead of the master, the slave was the first
compressor to start.
If the master compressor started first and, for any reason, trips during
operation, the master Fridgewatch 2100 Controller immediately requests
the slave compressor to start (if it is not already running). Operator
setting S8 Next Compressor Start Delay is not implemented in this case.
5.5.2.
Starting and Stopping the Slave Compressor
Assuming the master compressor starts first, when the master loads to
maximum capacity or limiting prevents the master loading further, the
slave compressor is started.
In a multi-compressor application, the master Fridgewatch 2100
Controller only requests the slave Fridgewatch Controller to start the first
compressor in the slave running order after all the compressors
controlled by the master controller are unavailable, i.e. at maximum load,
limiting or tripped.
Starting and stopping the slave compressor(s) is based on the principles
described in 5.4. Set Point Deviation, however, also refer to 5.5.3. below.
5.5.3.
Master/Slave Operation With a Fridgewatch 2100 Controller
Controlling More than One Compressor
Operator settings S12 Set Point Deviation to Start Next Compressor and
S13 Set Point Deviation to Stop Next Compressor can be configured as
the deviation from the set point that must be exceeded before any
start/stop action occurs, and are taken into account by the master
Fridgewatch Controller when starting and stopping the slave compressor.
However, when a master Fridgewatch 2100 Controller is linked to a slave
Fridgewatch 2100 Controller controlling more than one compressor, while
the set point deviation values can be applied by the master Fridgewatch
2100 Controller when starting the first slave compressor, these values
cannot be applied to the second and third compressors as it is the master
Fridgewatch 2100 Controller which measures the set point and start/stop
values - not the slave. Hence the slave Fridgewatch 2100 Controller
cannot know what deviation values to apply and can only start the next
compressor in the slave running order when loading instructions from the
master Fridgewatch 2100 Controller load the previous slave compressor
to maximum; the same applies when stopping slave compressors (other
than the last to stop). The starting and stopping of slave compressors is,
of course, subject to the slave Fridgewatch 2100 Controller next start and
stop delay timers.
5.6. Starting
and
Stopping the First Compressor
The final element in the control system relates to starting and stopping
the compressor. In the case of a multi-compressor application, this will
be the first compressor, compressor 1. Where Fridgewatch Controllers
are linked together in master/slave configuration, the first compressor to
start would normally be the one controlled by the master Fridgewatch
Controller; refer to 5.5.1. Starting the Master Compressor.
