Danfoss VLT 2010 Manual page 43

Appendix; PI Regulation
For inverse control; modification of the setpoint and
feedback signal is required.
Example:
A transmitter has a 0-15 foot span equal to 0-20mA. The
PID set-point must be set at 12 feet for inverse control.
• Enter 20-0 mA in parameter 413. The normal signal in
figure A is converted to an inverse signal as shown in
figure B.
mA
20
0 7.5 15 Ft
Figure A.
Normal signal from transmitter where
12 ft. represents 16mA (80%)
• Calculate the set point for inverse control.
Setpoint = 100 – (4/5 x 100) = 20%
It can be seen in figure C how the set point is calculated.
% Setpoint
100
Setpoint = 20%
0
Figure C.
Inverted signal from par:413 (current)
where 12 ft. represents 100%-80%=20%
• If the internal set-point is used, ensure that parameter
412 (voltage input) is set to no operation.
• The values in parameter 115 & 116 must be reversed.
The display at min. feedback in parameter 115 becomes
display at max. feedback and parameter 116 becomes
display at min. feedback.
• Connections and set-up are identical to normal control.
44
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%
100
0 7.5 15 Ft
Figure B.
Inverted signal from par:413
12 ft. represents 100%-80%=20%
12 15 Feet
External Setpoint
12
Link
27
16
18
+
50
53
55
–
55
–
+
60
VLT control terminals
Internal Setpoint
12
Link
27
16
18
50
53 Internal setpoint
parameter 205
55
Set parameter 412
to (no operation)
55
–
+
60
VLT control terminals
Start/Stop
Parameter 402 (start)
External setpoint
using potentiometer.
1 kOhm wire wound.
Parameter 412 (0-10V)
0/4-20 mA transmitter
parameter 413 (0/4-20mA)
Start/Stop
Parameter 402 (start)
0/4-20 mA transmitter
parameter 413 (0/4-20mA)