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Oil Pump Variable Speed Drive
2. During Automatic operation, if the Oil Pres sure
de creas es to < 15 PSID, a Safety shut down is per-
formed and OIL - LOW DIF FER EN TIAL PRES-
SURE is displayed. If it in creas es to >90 PSID, a
Safe ty shut down is per formed and OIL - HIGH
DIF FER EN TIAL PRESSURE is dis played.
The Microboard controls the VSD output frequency by
applying a Pulse Width Modulation (PWM) speed
command signal to the VSD. The signal is applied
ev ery 0.7 seconds. Within the 0.7 second period, the
du ra tion of time the signal is at logic low (<1VDC) and
logic high (+12VDC) level determines the VSD output
fre quen cy between 25 and 60 Hz. If it remains at a logic
high for the entire 0.7 second period, it is com mand ing
the VSD output frequency to be 25 Hz. If it is low for
the entire 0.7 second period, it is commanding the VSD
output frequency to be 60 Hz. Frequencies between these
extremes are achieved by driving the sig nal low for a
proportionate amount of time within the 0.7 sec ond
period. For example, if the signal is low for 50% (0.35
seconds) of the 0.7 second period, it would be command-
ing the VSD to operate at a frequency that is halfway
between 25 and 60 Hz, or 42.5 Hz. The res o lu tion, or
smallest increment of change is 0.01 sec onds. This al-
lows the output frequency to be changed in 0.5 Hz steps.
The VSD output frequency for any PWM input can be
calculated as follows:
Frequency in Hz = (On-Time in seconds / 0.02) + 25
The entire oil pump run time is divided into Oil Pres sure
Control Periods. They run consecutively and con tin u-
ous ly; when the fi rst one ends, the next one be gins, etc.
This repeats until the oil pump is shutdown. The dura-
tion of the periods is determined by the Control Period
Setpoint. This Setpoint is pro grammed in mul ti ples of
0.3 seconds over the range of 0.3 to 2.7 sec onds. At the
end of each period, the actual oil pres sure is compared
to the Oil Pressure Setpoint and the speed command is
changed as required to in voke VSD fre quen cy changes to
increase or decrease the oil pres sure. If the error between
the Oil Pressure Setpoint and the actual oil pressure is <
+6 PSID, the frequency is increased or decreased 0.5 Hz
to increase or decrease the oil pressure. However, if the
error is > + 6 PSID, the value programmed for Control
Pe ri od Setpoint determines the relative magnitude of
cor rec tion ap plied to the VSD output frequency. The
larg er the pro grammed value, the greater the amount of
cor rec tion above 0.5 Hz is applied.
96
To provide an operational status to the Microboard (via
I/O Board TB3-70), the VSD contains a set of nor mal ly
open (N.O.) relay contacts that are driven closed as long
as all the internal protection circuits are sat is fi ed. They
open anytime these circuits will not permit the VSD to
operate. The opening of these contacts ini tiate a chiller
cycling shutdown, displaying OIL - VARI ABLE
SPEED PUMP - DRIVE CONTACTS OPEN. After
the problem has cleared, the contacts au to mat i cal ly
close, except if the VSD experiences a short cir cuit on
the output; this requires the VSD to be man u al ly reset by
the removal and restoration of the VSD AC Power.
MANUAL OPERATION
The oil pump can be manually operated using the Oil
Sump Screen when logged in with SERVICE AC-
CESS lev el. While the chiller is running, the speed can
be man u al ly adjusted over the range of 25 to 60 Hz.
When the chiller is not running, manual on/off con trol,
as well as manual speed control is permitted. Af ter the
pump is manually turned on, it will au to mat i cal ly turn
off after 10 minutes of operation, if not man u al ly ter-
minated ear li er.
The RAISE and LOWER keys are used to increase
and decrease the VSD output frequency in 0.5 Hz
in cre ments. Each time the RAISE key is pressed, the
fre quen cy is increased 0.5 Hz. Each time the LOWER
key is pressed, the frequency is decreased 0.5 Hz. Re-
peat ed presses of these keys are required to increase or
decrease the frequency by greater amounts.
If the AUTO key is pressed, Automatic operation, as
described above, is resumed.
If the SET key is pressed, the VSD is driven to a spe cifi c
predetermined frequency. This permits service analysis
of the oil pressure at various oil pump speeds. This fre-
quency is programmed using instructions in the "System
Calibration, Service Setpoints and Reset Pro ce dures"
section of this book.
During Manual operation, the Oil Sump Screen can be
used to monitor the actual oil pressure and the speed
command.
FORM 160.54-M1(503)
YORK INTERNATIONAL
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