Example Of Closed-Loop Pid Control; Programming Order - Danfoss VLT HVAC Drive FC 102 Design Manual

Introduction
Up to eight preset references can be programmed in the
adjustable frequency drive. The active preset reference can
be selected using digital inputs or the serial communi-
cations bus. The reference can also be supplied externally,
most commonly from an analog input. This external source
is selected by one of the three reference source
parameters (3-15 Reference 1 Source, 3-16 Reference 2 Source
and 3-17 Reference 3 Source).
Digipot is a digital potentiometer. This is also commonly
called a Speed up/Slow control or a floating point control.
To set it up, program one digital input to increase the
reference while another digital input is programmed to
decrease the reference. A third digital input can be used to
reset the digipot reference. All reference resources and the
bus reference are added to produce the total external
reference. The external reference, the preset reference or
the sum of the two can be selected to be the active
reference. Finally, this reference can be scaled by using
3-14 Preset Relative Reference.
The scaled reference is calculated as follows:
Y
Reference = X + X ×
100
Where X is the external reference, the preset reference or
the sum of these and Y is 3-14 Preset Relative Reference in
[%].
If Y, 3-14 Preset Relative Reference is set to 0%, the
reference will not be affected by the scaling.

2.8.9 Example of Closed-loop PID Control

Figure 2.25 Closed-loop Control for a Ventilation System
MG16C122
Design Guide
In a ventilation system, maintain the temperature at a
constant value. The desired temperature is set between
23°F and 95°F [-5–+35°C] using a 0–10 volt potentiometer.
Because this is a cooling application, if the temperature is
above the setpoint value, increase the speed of the fan to
provide more cooling air flow. The temperature sensor has
a range of 14–104°F [-10–+40°C] and uses a two-wire
transmitter to provide a 4–20 mA signal. The output
frequency range of the adjustable frequency drive is 10 to
50 Hz.
1.
2.
3.

2.8.10 Programming Order

NOTICE!
This example assumes an induction motor is used, so
1-10 Motor Construction = [0] Asynchron.
Danfoss A/S © Rev. 2014-01-13 All rights reserved.
Start/Stop via the switch connected between
terminals 12 (+24 V) and 18.
Temperature reference via a potentiometer (23–
95°F [-5–+35 °C], 0–10 V) connected to the
following terminals:
•
50 (+10 V)
•
53 (input)
•
55 (common)
Temperature feedback via transmitter (14–104°F
[-10–40 °C], 4–20 mA) connected to terminal 54.
Switch S202 behind the LCP set to ON (current
input).
2 2
41