
RXB PLUS ROTARY SCREW COMPRESSOR UNITS
OPERATION
070.101-IOM (JAN 13)
Page 18
SETPOINTS DISPLAY, Page 1B:
Dead Band - This is a + (plus) or - (minus) value above or
below the setpoint at which the compressor will neither load
nor unload. A dead band of 1 is the default value. It is adjust-
able between .5 lb to 5 lb in increments of .5. The [Step] key
is used to select this setpoint; then press the [Change] key
to toggle through the selections.
Proportional Band - This setpoint is used to determine the
amount of time the load/unload solenoid is energized, ac-
cording to how far from the setpoint the actual control pres-
sure is. The smaller the number, the longer a load/unload
signal will be sent; 10% is the default value. Selections are
2, 5, 10, 15, 20, or 25%. The [Step] key is used to select
this setpoint; then press the [Change] key to toggle through
the selections.
Cycle Time - Cycle time is the amount of time between the
beginning of each load/unload response. Ten seconds is
the default value. “Cycle Time” is adjustable between 5 and
30 seconds in 5 second intervals. The [Step] key is used
to select a setpoint; then press the [Change] key to toggle
through the selections.
Low % FLA - This setpoint is used to determine if the coupling
has broken; 20% is the default value. It is adjustable from 0
to 100% FLA. Use the [Step] key to select a setpoint; then
enter the desired setpoint and press the [Enter] key.
SETPOINTS DISPLAY, Page 2:
MLC STOP LD - The Motor Load Control Stop Load, reported
as a percentage of the motor, full-load amps (FLA), will pre-
vent the compressor capacity control pistons from loading
when the setpoint is equaled or exceeded. NOTE: Consult
motor manufacturer for recommended setpoint.
MLC FORCE ULD - The motor Load Control Force Unload,
reported as a percentage of the motor, full-load amps (FLA),
will force the com pressor to unload until the motor, full-load
amps (FLA) fall within 1% of the setpoint or lower. NOTE: Con-
sult motor manufac turer for recom mended setpoint.
HI DISCH CUTOUT - The High Discharge Pres sure Cutout,
reported in pounds per square inch gauge (g), will shut down
the compressor if the discharge pressure equals or exceeds
this setpoint.
HI DISCH ALARM - The High Discharge Pressure Alarm,
reported in pounds per square inch gauge (g) will trigger a
prealarm if the discharge pres sure equals or exceeds this
setpoint.
CT FACTOR - The Current Transformer Factor records the
proper current transformer factor to match the compressor
motor FLA rating to the current trans former primary rating.
The CTF factor is program mable and its correct value is
determined by the following formula:
1024 x FLA (Full Load Amps *)
CTF =
10x CT (Current Transformer Primary Amps **)
* See motor nameplate.
** See CT located in starter panel.
EXAMPLE: FLA = 230 Amps
CT = 300 (300:5)
1024 x 230
CTF = = 78 (Round to whole number)
10 x 300
AUX 1 and AUX 2 - May be configured for either an alarm or
shutdown and with either a normally closed (NC) or normally
open (NO) contact.
TO CHANGE THE ADJUSTABLE SETPOINTS:
Adjustable Setpoints are stored in RAM (random access
memory) and are easily changed in the field.
Adjustable Setpoints are lost if
power is interrupted and the bat-
tery is not fully charged. To facili-
tate reentry, we suggest that a list of Adjustable Set-
points be affixed to one end of the microprocessor
cabinet for reference.
NOTE: The following procedure also applies to the
changing of the Security, Setback, and Auto Cycle dis-
play setpoints.
1. Press the [CHANGE] key to rotate the display to the Ad-
justable Setpoints display.
2. Press the [STEP] key to move or step a set of flashing
brackets through the various set points. A setpoint is selected
for change or update when it is enclosed by the flashing
brackets.
NOTE: The DAY indicator, itself, will flash when selec ted
for change or update.
3. Having selected the setpoint to be changed, the [NU-
MERIC KEYPAD] may be used to enter the new setpoint.
NOTE: All digits must be entered, including zeros. For
example, (01.0).
NOTE: The DAY, AUX 1, and AUX 2 setpoints, once selected,
are changed or updated by pressing the [CHAN GE] key.
NOTE: Certain setpoints may be reported in either pounds
per square inch gauge (g) or inches of mer cury (hg). To
toggle between (g) and (hg), having selected the setpoint,
press the [+/-] key to toggle between (g) and (hg).
4. In the event that an incorrect setpoint is keyed in com-
pletely or partially, press the [CLEAR] key to restore the
original setpoint. Pressing the [CLEAR] key a second time
will eliminate the flashing brackets.
5. Having keyed the desired setpoint, press the [ENTER] key.
The new setpoint will be entered and the flashing brackets
will move or step to the next setpoint.
NOTE: A setpoint entry outside the parameters of the
Adjustable Setpoint display will be refused and the
original Adjustable setpoint will be re stored.
NOTE: To clear any time values [STEP] to the desired
setpoint, press [CHANGE] and then press [CLEAR].
HOW TO DETERMINE
ADJUSTABLE SETPOINTS:
Adjustable Setpoints should reflect values compat ible with
normal system operation. Too high a Low Suction Pres sure
Alarm setpoint may cause nuisance prealarms. Similarly,
cutout setpoints should not fall within what are considered
normal plant oper ation. As a rule of thumb, set the Low Suc-
tion Pressure Alarm 5 PSIG lower than the lowest normal
suction pressure. The Low Suction Pressure Cutout should
be 5 to 10 PSIG lower than the Low Suction Pressure Alarm
setpoint.