The Remote Reference is comprised of:
•
Preset references.
•
External references (analog inputs,
pulse frequency inputs, digital po-
tentiometer inputs and serial com-
munication bus references).
•
The Preset relative reference.
•
Feedback controlled setpoint.
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 selec-
ted by one of the 3 Reference Source param-
eters (par. 3-15, 3-16 and 3-17). Digipot is a
digital potentiometer. This is also commonly
called a Speed Up/Speed Down 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
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 Refer-
ence. The External Reference, the Preset Ref-
erence or the sum of the two can be selected
to be the active reference. Finally, this refer-
ence can by be scaled using the Preset Rela-
tive Reference (par. 3-14).
The scaled reference is calculated as follows:
Reference
=
X
+
X
×
(
Y
100
)
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 [%].
NB!
If Y, the Preset Relative Reference (par. 3-14) is set to 0%, the reference will not
be affected by the scaling
2.9.4. Feedback Handling
A block diagram of how the drive processes the feedback signal is shown below.
Feedback handling can be configured to work with applications requiring advanced control, such
as multiple setpoints and multiple feedbacks. Three types of control are common.
VLT
®
HVAC Drive Design Guide
2. Introduction to VLT HVAC Drive
MG.11.B2.02 - VLT
®
is a registered Danfoss trademark
39
2
