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 | 85ºF |
Low Input Val | 50ºF |
User Ctrl SP | 75ºF |
Max User SP | 80ºF |
Min User SP | 70ºF |
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
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.
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