Frick QUANTUM - Compressor Sequence Overview (Mode 2)

The following setpoints are required for each compressor
to be sequenced:
Minimum Capacity when Running - This is the slide
valve position a compressor will continuously load to,
when started. The compressor will not unload below
this setpoint during normal system operation. The last
compressor that was signaled to start will be the first
compressor to unload to it’s Minimum Capacity when
Running setpoint. Once the compressor has unloaded
to this capacity position, a previous compressor is
then allowed to unload. When the Slide Valve is
above this setpoint + 1, the Slave sequence controller
energizes the Slide Valve > Minimum Capacity output.
Minimum Capacity to Stop Next Compressor - If
this compressor unloads to or below this setpoint and
the next compressor stop delay has timed out, then
the Slave Start output signal is de-energized to tell the
next compressor to stop. This compressor unloads to
this capacity position after the next compressor is
running at or below it’s Minimum Capacity when
Running setpoint.
Next Compressor Start Delay - The minimum time
in minutes that the actual capacity must be at or
above the starting capacity control setting before the
Master sequence controller will start it’s compressor.
Also, the minimum time in minutes that a compressor
must be at or above 98% slide valve position before
the Slave Start output signal is energized to start the
next compressor and the Capacity Up output signal is
energized to tell the next compressor to load. This
timer helps prevent cycling compressors on and off
due to short sudden changes in load within the
system. If the Master’s current reading falls below it’s
Capacity Control setpoint plus the Upper Dead Band
setpoint, the Master’s start time delay will be reset to
start counting again. If a running compressor’s slide
valve position falls below 98%, the start time delay for
starting the next compressor will be reset to start
counting again.
Next Compressor Stop Delay - The minimum time in
minutes that a running compressor must be at or
below the Minimum Capacity to Stop Next
Compressor slide valve position before the Slave
Start output is de-energized to signal the next
compressor to stop. This is also the minimum time in
minutes that the actual capacity must be at or below
the Capacity Control setpoint minus the Lower Dead
Band setpoint before the Master that has already
unloaded the compressor to at or below its Minimum
Capacity when Running setpoint + 1, will further
unload the compressor to below its Minimum Slide
Valve Position to Start setpoint, and then stop.
This timer helps prevent cycling compressors on and
off due to short sudden changes in load within the
system. If a running compressor’s Slide Valve position
rises above the Minimum Capacity to Stop Next
Compressor setpoint, the stop timer for stopping the
next compressor will be reset to start counting again.
And if the actual capacity rises above the Master’s
stopping Capacity Control setting, the Master’s stop
time delay counter will be reset to start counting again
A toggle key is provided for compressor sequencing:
[Compressor Sequencing Activate] - Selects to use
compressor sequencing to control this compressor.
The delay timers that are present when sequence
control is activated won’t change by simply changing
the setpoint. Sequence control must be de-activated
and then activated again.
[Compressor Sequencing De-Activate] - Selects to
not use compressor sequencing to control this
compressor. The Digital Board 2 outputs 1 through 3
and 8, are turned off.
A toggle key is provided for control type:
[Control Type Master] - Only one panel should be
selected as the Master. The Master compressor
sequence controller attempts to maintain it’s capacity
control setpoint by being the first compressor to start
and then loads and unloads in response to it’s
Capacity Control setpoints and furthermore will signal
the next panel (a Slave) to do likewise.
[Control Type Slave] - The Slave compressor
sequence controller is signaled from a previous panel
to load or unload, and then uses it’s capacity control
setpoints to determine when to pulse the panel’s local
Slide Valve load and Slide Valve unload outputs.
Compressor Sequence Overview (Mode 2)
The above settings are used to sequence the
compressors that have been setup for compressor
sequence control mode 2. The panels selected for
compressor sequence control mode 2 must be connected
via the proper hardware connection. Only a compressor
that is in both remote compressor mode and remote Slide
Valve mode and not in shutdown, will be started, stopped,
loaded or unloaded using this sequence control.
The refrigeration load refers to the demand for loading of
compressors to reduce the rise in capacity that has
resulted from an increased need for refrigeration in the
plant. When the load rises this means the capacity has
risen. When the load falls this means the capacity has
fallen. Compressors need to load if the Master sequence
controller’s capacity reading is above it’s Upper Dead
Band setpoint plus the Capacity Control setpoint and
compressors need to unload if the Master sequence
controller’s capacity reading is below it’s Capacity Control
setpoint minus the Lower Dead Band setpoint. During
compressor sequencing, if the Capacity Up output
(request to load the next compressor) is energized, then
the Capacity Down output (request to unload the next
compressor) is not energized; and likewise, if the Capacity
Down output is energized, then the Capacity Up output is
not energized.
If one of these compressors has been told to run but
remains off due to remaining Recycle Delay time or other
conditions preventing the compressor from running, then
no sequencing will happen until the compressor is running
or shutdown.
If one of these compressors is not in remote compressor
mode or is not in remote Slide Valve mode or is in
S90-010 O FRICK QUANTUM™ COMPRESSOR CONTROL PANEL
Page 56 OPERATION