Danfoss VLT HVAC Drive FC 100 Series Design Manual page 37

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VLT HVAC Drive Design Guide
The Remote Reference is comprised of:
• Preset references.
• External references (analog inputs, pulse frequency inputs, digital potentiometer inputs and serial communication 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 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/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 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 by be scaled using the Preset Relative Reference (par. 3-14).
The scaled reference is calculated as follows:
(
Reference = X + X ×
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
2.8.8. Feedback Handling
A block diagram of how the frequency converter 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.
Single Zone, Single Setpoint
Single Zone Single Setpoint is a basic configuration. Setpoint 1 is added to any other reference (if any, see Reference Handling) and the feedback signal
is selected using par. 20-20.
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Y
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2. Introduction to VLT HVAC Drive
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