Download AireLogic Digital Control System User Manual

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:
PID Select
High Input Val
Low Input Val
User Ctrl SP
Max User SP
Min User SP
Direct (as input increases output increases)
85ºF
50ºF
75ºF
80ºF
70ºF
The temperature transducer senses the supply air temperature and sends a corresponding
signal to the AireLogic 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% (010Vdc). 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.
Max User SP
80ºF
100%
Input > 75ºF?
override
scaler
0%
75ºF
User Ctrl SP
>
=
<
75ºF PID 0-100%
75ºF
100%
override
scaler
Input < 75ºF?
Min User SP
70ºF
0%
29
0-100%
Output