
RXF PLUS MICROPROCESSOR CONTROL PANEL S70-401 IOM
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START DELAY IN SECONDS -This is a common time de-
lay used between each step in the load sequence to ensure
that the need to add an additional compressor is justified.
This will prevent a compressor starting due to momentary
load surges.The timer only accumulates time whenever the
deadband is equaled or exceeded, and resets any time the
pressure or temperature falls below the “Start” setpoint.
STOP - The “Comp Stop” setpoint is the differential pres-
sureortemperaturebelow thesetpointthatmust be equaled
or exceeded before a compressor is taken off line. This
setpoint works in conjunction with the “Stop Delay” setpoint.
STOP DELAY IN SECONDS - This is a common time delay
used between each step in the unload sequence to ensure
that the need to stop a compressor is justified.This will pre-
vent the stopping of a compressor in response to a momen-
tary load dip and subsequently needing to restart it in a
short period oftime.The timeronly accumulates time when-
ever the pressure or temperature is equal to or below the
“Stop” setpoint, and resets any time the suction pressure
rises to within the “Stop” deadband.
MINIMUM SLIDE VALVE
COMP. #1 = 50 % SV
From this menu the operator may enter a minimum slide
valve setpoint for each compressor.
SEQUENCE SELECTION
COMP.#1 USES ID=01
This menu determines what compressors are to operate as
the #1=LEAD, #2=INTERMEDIATE and #3=LAG. A unique
ID code must be entered into the control panel of each com-
pressor. The ID codes do not have to be in any particular
sequence. However, for simplicity’s sake, it is usually best
to use the ID codes 01 for the lead compressor, 02 in the
intermediate, and 03 in the lag compressor. So, from this
menu the compressor #1 entry should show ID=01, com-
pressor #2’s entry should show ID=02, and compressor #3
should show ID=03.
NOTE: to change compressor sequence, the operator
must change either the ID codes on each compressor
or a better method would be to simply change the des-
ignated ID’s from this menu. Entering 00 will disable or
remove a given control ID code.
Example: compressor #1 running, compressor #2 ID’d to
00, and compressor #3 off. Should the sequence require
another compressor to come on line, then #2 would be
skipped and #3 would be started.
Notes:
a.Compressor designatedas #1 is always LEAD.Compres-
sordesignatedas#2 is always the INTERMEDIATE.Com-
pressor designated as #3 is always LAG.
b.For the compressor to be controlled it must be inREMOTE
start and have its capacity control selected to remote.
c.If the machine is failed, cutout, not in remote, or not lead
lag selected, then the compressor will not be controlled.
d.Any compressor below its minimum slide valve position
will be loaded for one second each minute to ensure that
they are within 5% of their minimum slide valve position.
If a compressor were allowed to unload further, it would
not allow proper load balance and correct compressor se-
quencing would be difficult.
COMPRESSOR SEQUENCING
NOTE: The following references to pressure also apply
to temperature since this is a temperature/pressure ca-
pable system.
On system start-up, as the high-stage pressure exceeds the
Start setpoint for the Start Time Delay period, compressor
#1 will come on line and modulate in response to pressure.
With #1 running:
If the load falls - #1 will unload to #1 Min SV setpoint. If the
suction pressure drops below the Stop setpoint for the Stop
Time Delay period, then #1 will turn off.
If the load rises - #1 will load up in response to pressure. If
the Start setpoint is exceeded for the Start time delay pe-
riod, then #2 will start.
With #1 and #2 running:
If the load falls - #2 will unload first to the #2 min. SV
setpoint, then #1 will unload to its #1 min. SV setpoint. If the
pressure drops below the Stop setpoint for the Stop time
delay period, then #2 will stop.
If the load rises - #1 and #2 will load up in response to
pressure. If the Start setpoint is exceeded for the Start time
delay period, then #3 will start.
With #1, #2, and #3 running:
If the load falls - #1 will remain fully loaded, #3 will unload
to the #3 min. SV setpoint, then #2 will unload to the #2 min.
SV setpoint. If the pressure drops below the Stop setpoint
for the Stop time delay period, then #3 will stop.
If the load rises - #1 will remain fully loaded, #2 and #3 will
load up in response to pressure.
Differences between the RXF Plus 3 Lead
Lag Program and the Standard RXF Plus
Control Program
As was mentioned in the beginning of the 3 Lead Lag sec-
tion, there are several differences between the lead lag and
thestandardversionof the RXF Plus control programs. With
the addition of the lead lag feature, the Setback feature was
removed. Pressing the [F3] key will jump you directly to the
lead lag control menus. It was also necessary to remove
the Auto-Cycle feature. Pressing the [F4] key will show an
appropriate message indicating this.
When using the lead lag program but not enabling the lead
lag feature, a minimal communications capability was re-
tained.TheInformationrequestcommand, the start and stop
commands, and the motor amps request commands were
left in the program.These commands are needed in situa-
tions where all program EPROM’s are of the lead lag ver-
sion. All other commands were removed.
OPERATION