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SECTION 18 - OIL PUMP VARIABLE SPEED DRIVE
b. If the oil pressure is less than the programmed
oil pressure setpoint and the speed command
is at 60Hz for 5 continuous seconds, any time
after the first 30 seconds of System run.
2. During automatic operation, if the oil pressure de-
creases to greater than or equal to 15 psid, a safety
shutdown is performed and OIL - LOW DIFFER-
ENTIAL PRESSURE is displayed. If it increases
to greater than or equal to 90 psid (120.0 psid with
software versions C.MLM.01.08.xxx (and later)
or C.OPT.01.08A.xxx (and later)), a safety shut-
down is performed and OIL - HIGH DIFFEREN-
TIAL PRESSURE is displayed.
The microboard controls the VSD output frequency
by applying a Pulse Width Modulation (PWM) speed
command signal to the VSD. The signal is applied
every 0.7 seconds. Within the 0.7 second period, the
duration of time the signal is at logic low (less than 1
VDC) and logic high (+12 VDC) level determines the
VSD output frequency between 25 and 60 Hz. If it re-
mains at a logic high for the entire 0.7 second period, it
is commanding the VSD output frequency to be 25 Hz.
If it is low for the entire 0.7 second period, it is com-
manding the VSD output frequency to be 60 Hz.
Frequencies between these extremes are achieved by
driving the signal low for a proportionate amount of
time within the 0.7 second period. For example, if the
signal is low for 50% (0.35 seconds) of the 0.7 second
period, it would be commanding the VSD to operate at
a frequency that is halfway between 25 and 60 Hz, or
42.5 Hz. The resolution, or smallest increment of change
is 0.01 seconds. This allows 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-
tinuously; when the first one ends, the next one begins,
etc. This repeats until the oil pump is shutdown. The
duration of the periods is determined by the Control
Period setpoint. This setpoint is programmed in multi-
ples of 0.3 seconds over the range of 0.3 to 2.7 seconds.
At the end of each period, the actual oil pressure is
compared to the Oil Pressure setpoint and the speed
command is changed as required to invoke VSD fre-
quency changes to increase or decrease the oil pres-
sure. If the error between the Oil Pressure setpoint and
the actual oil pressure is less than plus or minus 6 psid,
the frequency is increased or decreased 0.5 Hz to in-
172
crease or decrease the oil pressure. However, if the er-
ror is greater than plus or minus 6 psid, the value pro-
grammed for Control Period setpoint determines the
relative magnitude of correction applied to the VSD
output frequency. The larger the programmed value,
the greater the amount of correction above 0.5 Hz is
applied.
To provide an operational status to the microboard (via
I/O Board TB3-70), the VSD contains a set of normal-
ly open (N.O.) relay contacts that are driven closed as
long as all the internal protection circuits are satisfied.
They open anytime these circuits will not permit the
VSD to operate. The opening of these contacts initi-
ate a chiller cycling shutdown, displaying OIL - VARI-
ABLE SPEED PUMP - DRIVE CONTACTS OPEN.
After the problem has cleared, the contacts automati-
cally close, except if the VSD experiences a short cir-
cuit on the output; this requires the VSD to be manu-
ally 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 level. While the chiller is running, the speed can
be manually adjusted over the range of 25 to 60Hz.
When the chiller is not running, manual ON/OFF con-
trol, as well as manual speed control is permitted. After
the pump is manually turned ON, it will automatically
turn OFF after 10 minutes of operation, if not manually
terminated earlier.
The RAISE and LOWER keys are used to increase and
decrease the VSD output frequency in 0.5Hz incre-
ments. Each time the RAISE key is pressed, the fre-
quency is increased 0.5Hz. Each time the LOWER key
is pressed, the frequency is decreased 0.5Hz. Repeated
presses of these keys are required to increase or de-
crease 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 specific
predetermined frequency. This permits service analysis
of the oil pressure at various oil pump speeds. This fre-
quency is programmed using instructions in SECTION
33 - SYSTEM CALIBRATION, SERVICE SETPOINTS,
AND RESET PROCEDURES of this manual.
During Manual operation, the OIL SUMP Screen can
be used to monitor the actual oil pressure and the speed
command.
JCI COMPANY CONFIDENTIAL
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
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