NB!
If a feedback is not used, its source must be set to
No Function
[0]. Par. 20-20
Feedback Function
determines how the three possible
feedbacks will be used by the PID Controller.
20-01 Feedback 1 Conversion
Option: Function:
This parameter allows a conversion function to be applied to Feedback 1.
[0] * Linear
Linear
[0] has no effect on the feedback.
[1] Square root
Square root
[1] is commonly used when a pressure sensor is used to provide flow feedback
(
(
flow
∝
pressure
)).
[2] Pressure to temperature
Pressure to temperature
[2] is used in compressor applications to provide temperature feedback
using a pressure sensor. The temperature of the refrigerant is calculated using the following for-
mula:
Temperature
=
A
2
(
ln
(
Pe
+ 1
)
−
A
1
)
−
A
3, where A1, A2 and A3 are refrigerant-specific con-
stants. The refrigerant must be selected in par. 20-30
Refrigerant
. Par. 20-21
Setpoint 1
through
par. 20-23
Setpoint 3
allow the values of A1, A2 and A3 to be entered for a refrigerant that is not
listed in par. 20-30
Refrigerant
.
[3] Pressure to flow Pressure to flow is used in applications where the air flow in a duct is to be controlled. The feedback
signal is represented by a dynamic pressure measurement (pitot tube).
Flow
=
Duct
Area
×
Dynamic
Pressure
×
Air
Density
Factor
See also par. 20-34
Duct 1 Area [m2]
through par. 20-38
Air Density Factor [%]
for setting of duct
area and air density.
[4] Velocity to flow Velocity to flow is used in applications where the air flow in a duct is to be controlled. The feedback
signal is represented by an air velocity measurement.
Flow
=
Duct
Area
×
Air
Velocity
See also par. 20-34
Duct 1 Area [m2]
through par. 20-37
Duct 2 Area [in2]
for setting of duct area.
20-03 Feedback 2 Source
Option: Function:
See par. 20-00
Feedback 1 Source
for details.
[0] * No function
[1] Analog input 53
[2] Analog input 54
[3] Pulse input 29
[4] Pulse input 33
[7] Analog input X30/11
[8] Analog input X30/12
[9] Analog Input X42/1
[10] Analog Input X42/3
[11] Analog Input X42/5
[100] Bus feedback 1
[101] Bus feedback 2
[102] Bus feedback 3
VLT HVAC Low Harmonic Drive Operating In-
structions 6 How to Programme the Low Harmonic Drive
MG.16.A1.02 - VLT
®
is a registered Danfoss trademark 111
6
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