FRICK QUANTUM CONTROL PANEL
OPERATION
S90-010 O
Page 39
Compressor Sequence Status
The active Capacity Control setpoints and Capacity Con-
trol reading are only shown here for referencing.
The following data is displayed for each compressor to be
sequenced:
• Slide Valve %
• 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 Start
• Off 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
The above settings are used to sequence the selected com-
pressors. Only a compressor that is in both remote com-
pressor 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 compres-
sors in an energy efficient method and provides a smooth
transition from one compressor to another, while also giv-
ing operator flexibility.
The deadband determines how quickly the system will re-
spond 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” set-
point, or lengthening the “Stop Time Delay”, or lengthening
the “Minimum Run Time” can be used to prevent a com-
pressor 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 mi-
nus 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 situ-
ation which requires 3 minutes for each available compres-
sor. If there are 4 compressors, the delay will be 12 minutes.
When this message is cleared, the compressor is again
available for sequencing.
The following is an example of sequencing compressors:
On System Start-up - The first available compressor
in the order of “A”, “B”, “C”, and “D” will start if the ca-
pacity is greater than or equal to the “Start” setpoint for
it’s “Start Delay” time period. If “A” is not available then
“B” will start when it’s “Start Delay” has timed out. If “B”
is not available then “C” will start when it’s “Start Delay”
has timed out. If “C” is not available then “D” will start
when it’s “Start Delay” has timed out.
On an initial or cold start-up (no compressors are run-
ning) and “Load Limiting” has been enabled, then the
first compressor started will load to the “Load Limiting
Slide Valve Position” setpoint and remain there until
the “Load Limiting Duration Time” has timed out or until
the current reading of the process variable falls below
the “Start” setpoint.
Load Rises - If the current reading continues to be
greater than or equal to the “Capacity Control” setpoint
plus the “Upper Dead Band” setpoint, then the first com-
pressor in the order of “A”, “B”, “C”, and “D” that is run-
ning will be loaded to 100%, followed by the next run-
ning compressor in the sequencing. When at 100%,
the load signal will be sent to that compressor every
minute to ensure the compressor remains fully loaded.
If all running compressors are loaded greater than 90%
slide valve position, then the next available compres-
sor in the order of “A”, “B”, “C”, and “D” will be started if
the current reading of the process variable is greater
than the “Start” setpoint for it’s “Start Delay” time.
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