Trane DFIA Programming Manual page 21

MUA-SVP01A-EN • Direct-Fired Indoor and Outdoor Units
Functions
to the Max User setpoint. In this situation the output value is the greater of the
PID output or the override output.
If the input variable is below the User Control setpoint, the output could decrease
from 100% to 0% as the input variable decreases from the User Control setpoint
to the Min User setpoint. In this situation the output value is the lesser of the PID
utput or the override output. See the following example.
Assume the user wishes to control a chilled water valve using a temperature
transducer. The control variable will be supply air temperature. As the supply air
temperature increases, the chilled water valve should open to lower the
temperature. The temperature transducer has a range of 50ºF - 85ºF . The user
would like the supply air temperature to be 75ºF but does not want it to drop
below 70ºF or go above 80ºF . The parameters entered on the keypad display will
be:
Direct (as input increases
PID Select output increases)
High Input Val
Low Input Val
User Ctrl SP
Max User SP
Min User SP
The temperature transducer senses the supply air temperature and sends a
corresponding signal to the AdaptAire controller. The controller compares this
signal to the desired user control setpoint (75ºF) and uses the PID loop to
modulate the output from 0-100% (0-10Vdc). The output is connected to the
chilled water valve that opens or closes to maintain the specified supply air
temperature.
If the supply air temperature is 75ºF , the output from the controller will be
determined by the PID control sequence, and the override will have no effect on
the output.
If the supply air temperature is more than 75ºF , the output from the controller will
be determined by the PID control sequence or the override whichever is less.
If the supply air temperature is less than 75ºF , the output from the controller will
be determined by the PID control sequence or the override whichever is more.
85ºF
50ºF
75ºF
80ºF
70ºF
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