Danfoss VLT Series Design Manual page 39

VLT ® HVAC Drive Design Guide
2.8.3. Example of Closed-loop PID Control
The following is an example of a closed-loop control for a ventilation system:
In a ventilation system, the temperature is to be maintained at a constant value. The desired
temperature is set between 23° and 95° F [-5° and +35° C] using a 0-10 volt potentiometer.
Because this is a cooling application, if the temperature is above the setpoint value, the speed of
the fan must be increased to provide more cooling air flow. The temperature sensor has a range
of 14° to 104° F [-10° to +40° C] and uses a two-wire transmitter to provide a 4-20 mA signal.
The output frequency range of the drive is 10 to 50 Hz.
1. Start/Stop via switch connected between
terminals 12 (+24 V) and 18.
2. Temperature reference via a potentiome-
ter (23°- 95° F [-5° to +35° C], 0 10 V)
connected to terminals 50 (+10 V), 53 (in-
put) and 55 (common).
3. Temperature feedback via transmitter
(14°-104° F [-10° - +40° C], 4-20 mA)
connected to terminal 54. Switch S202 be-
hind the local control panel set to ON (cur-
rent input).
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
2. Introduction to the VLT HVAC Drive
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