shutdown, that compressor is not available to be
sequenced. However, it will signal its Capacity Control
requirements to the next compressor.
Because the next compressor is forced to load to the
Minimum Capacity when Running setpoint, excess
capacity could occur causing the previous compressor to
adjust by unloading a little. If the load continues to rise
then the previous compressor that unloaded to below 98%
will load again to at or above 98% prior to signaling the
next compressor to load.
The following is an example of sequencing compressors:
On System Start-up - The Master compressor will
start if the capacity is greater than or equal to the
Upper Dead Band plus the Capacity Control setpoint
for the Next Compressor Start Delay time period. If
the Master is not available to be sequenced, then the
Master’s Start Slave output and Capacity Up output
are energized. If the Slave with the Start Slave input
and the Capacity Up input energized is not available
to be sequenced, then the Slave’s Start Slave output
and Capacity Up output are energized.
On an initial start-up of a compressor, the compressor
started will load to the Minimum Capacity when
Running setpoint and remain at or above this setpoint
until stopping. A Slave sequence controller energizes
the Slide Valve > Minimum Capacity output when the
Slide Valve is above the Minimum Capacity when
Running setpoint + 1.
Load Rises - If the Actual reading continues to be
greater than or equal to the Upper Dead Band plus
the Capacity Control setpoint at the Master sequence
controller, then the first available compressor in the
order the panels are wired, starting with the Master
sequence control panel is selected to load to 100%,
followed by the next compressor.
If the running compressor loads to at or above 98%
Slide Valve position for the Next Compressor Start
Delay time period, then the Start Slave output and
Capacity Up output are energized.
Load Falls - If the Actual reading falls to or below the
Capacity Control setpoint minus the Lower Dead
Band setpoint at the Master sequence controller, then
the last compressor that is running will be selected for
unloading. If the Start Slave output is energized
(indicating another compressor has been told to run)
the Capacity Down output is energized. If the Start
Slave output is not energized and the Capacity Down
input is energized then this compressor is unloaded to
it’s Minimum Capacity when Running setpoint. If the
Start Slave output is energized and the Slide Valve >
Minimum Capacity input is not energized (indicating
the next compressor has been unloaded to at or
below the Minimum Capacity when Running setpoint)
then this compressor is unloaded to or below its
Minimum Capacity to Stop Next Compressor setpoint.
When the Next Compressor Stop Delay has timed
out, then the Start Slave and Capacity Down outputs
are de-energized.
A running compressor that is signaled to stop will
unload to or below it’s Highest Slide Valve Position to
allow starting the compressor setpoint and then will
stop. The Master sequence controller is the last
compressor to unload. The Master will unload the
compressor to the Minimum Capacity when Running
setpoint and if the Master’s stop delay has timed out,
the Master will unload the compressor to it’s Highest
Slide Valve Position to allow starting the compressor
setpoint before stopping this compressor.
COMPRESSOR SEQUENCE CONTROL - MODE 2 WIRING
Grammatic 2502 Grammatic 1502
Digital Board 2
P1-1 Output 1 Start / Slave Start DI-4 Input 4
P1-2 Output 2 Capacity Up / Slave Capacity Up DI-5 Input 5
P1-3 +24 VDC Input from Gram +24 VDC Digital Supply
P1-5 Output 3 Capacity Down / Slave Capacity Down DI-6 Input 6
P1-6 Input 4 Slide Valve > Minimum /Capacity > Minimum DI-2 Input 2
P2-1 Input 5 Start / Slave Start DO-7 Output 19
P2-2 Input 6 Capacity Up / Slave Capacity Up DO-8 Output 20
+24 VDC (Quantum™ Supply) to Digital Output Relay Common
P2-4 to +24 VDC Return
(Quantum™ Supply)
No Connection
P2-5 Input 7 Capacity Down / Slave Capacity Down DO-9 Output 21
P2-6 Output 8 Slide Valve > Minimum / Capacity > Minimum DO-10 Output 22
Note: Use ODCM-5, 5 V digital output modules and IDCM-5, 5 V digital input modules.
FRICK
QUANTUM™ COMPRESSOR CONTROL PANEL S90-010 O
OPERATION Page 57
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