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There are 2 methods of ramp loading with the PIC. Ramp loading can be based on chilled
water temperature or on motor load.
1. Temperature ramp loading
limits the rate at which either leaving chilled water or entering
chilled water temperature decreases by an operator-configured rate. The lowest
temperature ramp table will be used the first time the machine is started (at
commissioning). The lowest temperature ramp rate will also be used if machine power has
been off for 3 hours or more (even if the motor ramp load is selected).
2. Motor load ramp loading
limits the rate at which the compressor motor current or
compressor motor load increases by an operator-configured rate.
The
TEMP (Temperature) PULLDOWN, LOAD PULL DOWN,
and
SELECT RAMP TYPE
may be viewed/modified on the LID Equipment Configuration table, Config table (see Table 2).
Motor load is the default type.
Capacity Override (See
Table 4
)
These can prevent some safety shutdowns caused by exceeding motor amperage limit,
refrigerant low temperature safety limit, motor high temperature safety limit, and condenser high
pressure limit. In all cases there are 2 stages of compressor vane control.
1. The vanes are held from opening further, and the status line on the LID indicates the reason
for the override.
2. The vanes are closed until condition decreases below the first step set point, and then the
vanes are released to normal capacity control.