Section 3 – SR-2 Software Description
Controlling Sensor
Micro Rev
All
HMI Rev
All
Choices
Return, Discharge or Selectable
Factory Set
Return
Exceptions
Description Modulation provides very smooth
and steady temperature control. Modulation is only
operational in Continuous Mode.
This feature determines the controlling sensor used
during modulation operation, either the Return Air
Temperature Sensor or Discharge Air Temperature
Sensor.
During Return Air Modulation, the discharge air
temperature is limited to the programmed floor limit.
The floor limit is equal to setpoint minus the setting
of the FreshSet Floor Limit feature. This provides
additional protection from freezing for sensitive
loads. If the discharge air temperature reaches the
floor limit, unit control will shift to the discharge air
sensor. Control will automatically revert to the return
air sensor when conditions allow.
During Discharge Air Modulation, the discharge air
temperature is controlled to the setpoint.
Although the Selectable choice appears in the
menu, it is not implemented and should not be used.
FreshSet Modulation Pull Down Option
Micro Rev
All
HMI Rev
All
Choices
Maximum or Floor Limit
Factory Set
Maximum
Exceptions Only appears if Controlling Sensor =
Return.
Description This feature determines the
modulation pull down control algorithm used. This
feature is only available with return air temperature
control. The floor limit algorithm is always used with
discharge air control.
If MAX is selected, modulation pull down control is
governed by the 300°F*Minute (160°C*Minute)
algorithm. During MAX pull down, the unit is in full
cool and the discharge air temperature is allowed to
drop below the programmed floor limit for a defined
period of time. This option provides the fastest pull
down while minimizing the potential for product top
freezing.
MAX pull down example: If the discharge air is 15°F
(8°C) below setpoint the unit will operate in full cool
for 20 minutes before entering modulation cool.
(e.g. 15°F x 20 minutes = 300°F*Minutes or 8°C x 20
minutes = 160°C*Minutes)
If FLOOR LIMIT is selected, modulation pull down
control is governed by the Floor Limit pull down
algorithm. During Floor Limit pull down the unit will
operate in high speed but will control the discharge
air temperature to the programmed Floor Limit.
After the pull down conditions are satisfied the unit
will switch to low speed modulation. This option
provides a fast pull down while eliminating the
potential for product top freezing with fragile
commodities.
3-37
31 January 2005
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