FRICK QUANTUM CONTROL PANEL
OPERATION
S90-010 O
Page 38
The load limiting setpoints are used if no compressors are
running and the equalized system is to be slowly pulled
down to normal. These setpoints limit the compressor load-
ing when first starting a compressor:
Slide Valve Position - the Slide Valve position setpoint
that the control system will hold the Slide Valve until the
duration timer has timed out.
Duration Time - the amount of time in minutes to hold
the compressor at the “Load Limiting Slide Valve Posi-
tion” setpoint. If load limiting is not desired, set this time
to zero (0).
When the first compressor is started, the sequence will
allow that compressor to load up to the “Slide Valve
Position” setpoint and hold the compressor at this set-
point until the “Duration Time” has timed out or the
current reading of the process variable falls below the
“Start” setpoint.
The following set points are required for each compressor
on the suction level:
(A - D) Compressor ID - A through D represent the
sequence position. Any machine can be set for any
sequence position. The letter determines the starting
order of the compressors, position A is the first position.
If the “Start” setpoint is maintained, the lead or first
machine started, will always load up first and then the
next sequence position on up as they are needed. The
stopping of compressors is done in the reverse order
of the starting. The compressor ID# should be entered
in the proper sequence position for the suction level it
is located on. Each compressor must have a unique
ID# entered at their control panel. A zero (0) disables
or removes a compressor ID from being sequenced.
Unload Minimum Slide Valve Position - This is the
Slide Valve position a compressor will be allowed to
unload to. The compressors will unload to the mini-
mum Slide Valve position for that machine, when the
reading is below the Capacity Control lower deadband.
This set point is only used if more than one compressor
is running. When only one compressor is running it is
allowed to fully unload. This set point can prevent short
cycling of compressors in the unload sequence. Short
cycling occurs when a compressor is stopped and the
current reading quickly rises and an already running
compressor is unable to compensate because it is run-
ning at full load, so a compressor is cycled back on
very shortly after a compressor was stopped. A screw
compressor has some minimum built-in capacity that
cannot be shed, generally in the range of 10-15% of
full load capacity, when the compressor is stopped the
control system needs to compensate for this loss. If a
compressor that is running at full load is allowed to
unload to a minimum slide valve position, this com-
pressor will then be able to compensate for the extra
load that occurs when another compressor is stopped.
The computer will not unload a compressor below this
set point during normal system operation. For example,
if compressor “A” is running at 100 % capacity and
compressor “B” is running and has been unloaded to
the minimum Slide Valve position, “B” is still contribut-
ing somewhat to the capacity. To take “B” off line would
be to lose approximately 10% of the total capacity. If
“A” was already loaded to 100% capacity, it would not
be able to load to compensate for losing the 10% “B”
dropped off. The current reading would rise and “B”
would be cycled on again. If the current reading re-
mains low (below the lower deadband) for the prede-
termined time (stop time delay), “B” will then stop. “A”
will have sufficient reserve capacity to maintain the
loss of “B”. The control of this set point is in percentage
of Slide Valve, not compressor capacity. With some
experimentation, it is possible to find the right value for
the minimum Slide Valve position set points that nei-
ther undercompensate for the built-in capacity, result-
ing in short cycling of the compressors, nor overcom-
pensates for the built-in capacity, resulting in inefficient
operation (where the sum of the capacity of the com-
pressors that are running is significantly less than the
full load capacity of the next compressor in the unload
sequence).
Start Time Delay - The minimum time in minutes that
the current reading must be at or above the “Start” set-
point before a compressor will start. This timer helps
prevent cycling compressors on and off due to short
sudden changes in load within the system. If the cur-
rent reading falls below the “Start” setpoint for any rea-
son at any time, the start time delay will be reset to start
counting again if needed. When a compressor is start-
ing, the start time delays will be reset to start counting
again if needed for a next compressor.
Stop Time Delay - The minimum time in minutes that
the current reading must be at or below the “Stop set-
point before a compressor will stop. This timer helps
prevent cycling compressors on and off due to short
sudden changes in load within the system. If the cur-
rent reading rises above the “Stop” setpoint for any
reason at any time, the stop time delay counter will be
reset to start counting again if needed. When a com-
pressor is stopping, the stop time delays will be reset to
start counting again if needed for a next compressor.
Minimum Run Time - the minimum time in minutes that
the compressor must run before it is allowed to stop.
This time should be as long as the Recycle Delay time.
If the compressor has run out its Recycle Delay time
and is turned off it will still be available to run as soon
as required.
A toggle key is provided for compressor sequencing:
[Activate] - Selects the compressor control to be cur-
rently active.
[De-Activate] - Selects the compressor control to be
currently not active.
Note: Only one panel should have Compressor Se-
quencing active.
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