Danfoss VLT Series Design Manual page 44

2. Introduction to the VLT HVAC Drive
The Remote Reference is comprised of:
•
2 •
•
•
Up to 8 preset references can be programmed in the drive. The active preset reference can be
selected using digital inputs or the serial communications bus. The reference can also be supplied
externally, most commonly from an analog input. This external source is selected by one of the 3
reference source parameters (par. 3-15, 3-16 and 3-17). Digipot is a digital potentiometer. This
is also commonly called a speed up/slow control, or a floating point control. To set it up, one digital
input is programmed to increase the reference, while another digital input is programmed to de-
crease 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 the preset relative reference (par. 3-14).
The scaled reference is calculated as follows:
Reference
Where X is the external reference, the preset reference or the sum of these, and Y is the preset
relative reference (par. 3-14) in [%].
44
Preset references.
External references (analog inputs, pulse frequency inputs, digital potentiometer inputs
and serial communication bus references).
The preset relative reference.
Feedback controlled setpoint.
( )
Y
= X + X ×
100
NOTE
If Y, the preset relative reference (par. 3-14), is set to 0%, the reference will not be
affected by the scaling
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
VLT ® HVAC Drive Design Guide