Frick QUANTUM - Compressor Sequence Overview (Mode 1)

Stop Time Delay - The minimum time in minutes that
the current reading must be at or below the Stop
setpoint 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
current 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
compressor 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
currently active.
[De-Activate] - Selects the compressor control to be
currently not active.
Note: Only 1 panel should have Compressor
Sequencing active.
Compressor Sequence Status
The active Capacity Control setpoints and Capacity
Control reading are only shown here for referencing.
The following data is displayed for each compressor to be
sequenced:
Slide Valve % - The actual % reading of the Slide
Valve position.
Slide Valve Status - One of the following could be
shown:
• Load - Indicates the compressor is being
told to load.
• Unload - Indicates the compressor is being
told to unload
• Idle - Indicates the compressor is neither
being told to load or unload.
Note: The displayed status does not necessarily
reflect the current solenoid status.
Sequence Status - One of the following text strings
could be shown:
• Off in Remote Start
• Off in Manual Start
• Off in Autocycle StartOff in Recycle Delay
• Shutdown
• Running in Remote Start
• Running in Manual Start
• Running in Autocycle Start
• Not Communicating
• Not in Remote Start
• Slide Valve not in Remote
• Unable to Start
• Starting
Compressor Sequence Overview (Mode 1)
The above settings are used to sequence the selected
compressors. Only a compressor that is in both remote
compressor mode and remote Slide Valve mode will be
started, stopped, loaded or unloaded using this sequence
control. If one of these compressors is failed, shutdown
(cutout), in Recycle Delay, or unable to communicate, that
compressor will be skipped and the next compressor in
the sequence (if there is one) will be controlled.
Compressor Sequencing allows for staging the
compressors in an energy efficient method and providing a
smooth transition from one compressor to another, while
also giving operator flexibility.
The deadband determines how quickly the system will
respond to a change in the process. For an example, a
booster compressor might have a deadband of 0.5 PSIG
for a quicker response than the high stage compressor
with a deadband of 1.0 PSIG.
The proportional band and the cycle time determine how
smoothly the compressor loads or unloads, and can be
used to prevent overshooting the process setpoint.
Lowering the Unload Minimum Slide Valve Position
setpoint, or lengthening the Stop Time Delay, or
lengthening the Minimum Run Time can be used to
prevent a compressor from cycling off and on too quickly.
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 Current Value is
greater than or equal to the Capacity Control setpoint plus
the Upper Dead Band setpoint and they need to be
unloaded if the Current Value is less than or equal to the
Capacity Control setpoint minus the Lower Dead Band
setpoint.
When starting a compressor, a start command is sent from
the panel that has Compressor Sequencing activated to
the selected compressor every 30 seconds for 3 minutes.
Should the compressor not start in that time period, the
sequence status message Unable to Start is shown. If this
occurs, the next compressor in the sequence (if there is
one) will be sent the start command when it’s Start Delay
times out. The Unable to Start message will clear after a
time delay. The time delay is based on the worst case
situation which requires 3 minutes for each available
compressor. If there are 4 compressors, the delay will be
12 minutes. When this message is cleared, the
compressor is again available for sequencing.
S90-010 O FRICK QUANTUM™ COMPRESSOR CONTROL PANEL
Page 52 OPERATION