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CONFIGURATION table. See Table 3, Example 14. SCHED-
ULE NUMBER can be changed to any value from 03 to 99. If
this number is changed on the NET_OPT screen, the operator
must go to the ATTACH TO NETWORK DEVICE screen to
upload the new number into the SCHEDULE screen. See
Fig. 21.
Safety Controls —
The PIC II monitors all safety control
inputs and, if required, shuts down the chiller or limits the slide
valve to protect the chiller from possible damage from any of
the following conditions:
• high motor winding temperature
• high discharge temperature
• low discharge superheat temperature TC (frame 1 and 2)
compressor chillers*
• low oil pressure
• low cooler refrigerant temperature
• condenser high pressure or low pressure
• inadequate water/brine cooler and condenser flow
• high, low, or loss of voltage
• ground fault (option)
• high oil filter pressure drop
• low oil level
• voltage imbalance
• current imbalance
• excessive motor acceleration time
• excessive starter transition time
• lack of motor current signal
• excessive motor amps
• excessive compressor stall
• temperature sensor and transducer faults
*Superheat is the difference between saturation temperature and sen-
sible temperature. The high discharge temperature safety measures
only sensible temperature.
Starter faults or optional protective devices within the starter
can shut down the chiller. The protective devices you have for
your application depend on what options were purchased.
If compressor motor overload occurs, check the motor for
grounded or open phases before attempting a restart
If the PIC II control initiates a safety shutdown, it displays
the reason for the shutdown (the fault) on the CVC display
screen along with a primary and secondary message, energizes
an alarm relay in the starter, and blinks the alarm light on the
control panel. The alarm is stored in memory and can be
viewed on the ALARM HISTORY and ISM_HIST screens on
the CVC, along with a message for troubleshooting. If the safe-
ty shutdown was also initiated by a fault detected in the motor
starter, the conditions at the time of the fault will be stored in
ISM_HIST.
To give more precise information or warnings on the chill-
er's operating condition, the operator can define alert limits on
various monitored inputs. Safety contact and alert limits are de-
fined in Table 4. Alarm and alert messages are listed in the
Troubleshooting Guide section, page 76.
Shunt Trip (Option) —
option on the PIC II is to act as a safety trip. The shunt trip is
wired from an output on the ISM to a shunt trip equipped mo-
tor circuit breaker. If the PIC II tries to shut down the compres-
sor using a normal shutdown procedure but is unsuccessful for
30 seconds, the shunt trip output is energized and causes the
circuit breaker to trip off. If ground fault protection has been
applied to the starter, the ground fault trip also energizes the
shunt trip to trip the circuit breaker. Protective devices in the
starter can also energize the shunt trip. The shunt trip feature
can be tested using the Control Test feature.
The function of the shunt trip
Default Screen Freeze —
alarm state, the default CVC display "freezes," that is, it stops
updating. The first line of the CVC default screen displays a
primary alarm message; the second line displays a secondary
alarm message.
The CVC default screen freezes to enable the operator to
see the conditions of the chiller at the time of the alarm. If the
value in alarm is one normally displayed on the default screen,
it flashes between normal and reverse video. The CVC default
screen remains frozen until the condition that caused the alarm
is remedied by the operator.
Knowledge of the operating state of the chiller at the time an
alarm occurs is useful when troubleshooting. Additional chiller
information can be viewed on the status screens and the
ISM_HIST screen. Troubleshooting information is recorded in
the ALARM HISTORY table, which can be accessed from the
SERVICE menu.
To determine what caused the alarm, the operator should
read both the primary and secondary default screen messages,
as well as the alarm history. The primary message indicates the
most recent alarm condition. The secondary message gives
more detail on the alarm condition. Since there may be more
than one alarm condition, another alarm message may appear
after the first condition is cleared. Check the ALARM HISTO-
RY screen for additional help in determining the reasons for the
alarms. Once all existing alarms are cleared (by pressing the
softkey), the default CVC display returns to normal
RESET
operation.
Ramp Loading —
down the rate at which the compressor loads up. This control
can prevent the compressor from loading up during the short
period of time when the chiller is started and the chilled water
loop has to be brought down to CONTROL POINT. This helps
reduce electrical demand charges by slowly bringing the
chilled water to CONTROL POINT.
There are two methods of ramp loading with the PIC II.
Ramp loading can be based on chilled water temperature or on
motor load. Either method is selected from the RAMP__DEM
screen.
1. Temperature ramp loading (TEMP PULLDOWN DEG/
MIN) limits the degrees per minute rate at which either
leaving chilled water or entering chilled water temper-
ature decreases. This rate is configured by the operator
on the TEMP_CTL screen. The lowest temperature
ramp rate will also be used if chiller power has been
off for 3 hours or more (even if the motor ramp load is
selected as the ramp loading method.
2. Motor load ramp loading (LOAD PULLDOWN) limits
the degrees per minute rate at which the compressor
motor current or compressor motor load increases. The
LOAD PULLDOWN rate is configured by the operator
on the RAMP_DEM screen in amps or kilowatts.
If kilowatts is selected for the DEMAND LIMIT SOURCE,
the MOTOR RATED KILOWATTS must be entered (informa-
tion found on the chiller Requisition form).
The TEMP PULLDOWN DEG/MIN may be viewed or
modified on the TEMP_CTL screen which is accessed from
the EQUIPMENT SERVICE screen. PULLDOWN RAMP
TYPE, DEMAND LIMIT SOURCE, and MOTOR LOAD
RAMP %/MIN may be viewed or modified on the
RAMP_DEM screen.
Capacity Override (Table 5) —
can prevent some safety shutdowns caused by exceeding the
motor amperage limit, refrigerant low temperature safety limit,
motor high temperature safety limit, and condenser high pres-
sure limit. In all cases, there are 2 stages of compressor slide
valve control.
38
When the chiller is in an
The ramp loading control slows
Capacity overrides
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