Danfoss VLT Series Programming Manual page 148

Parameter Description
NOTE
Carry out No Flow tuning before setting the PI controller parameters!
FC
P
No Flow Detection is based on the measurement of speed and power. For a certain speed the frequency converter calculates
the power at no flow.
This coherence is based on the adjustment of two sets of speed and associated power at no flow. By monitoring the power
it is possible to detect no flow conditions in systems with fluctuating suction pressure or if the pump has a flat charac-
teristic towards low speed.
The two sets of data must be based on measurement of power at approx. 50% and 85% of maximum speed with the
valve(s) closed. The data are programmed in the parameter group 22-3*. It is also possible to run a Low Power Auto Set Up
(22-20 Low Power Auto Set-up) automatically stepping through the commissioning process and also automatically storing the
data measured. The frequency converter must be set for Open Loop in 1-00 Configuration Mode, when carrying out the Auto
Set Up (See No Flow Tuning parameter group 22-3*).
NOTE
If to use the integrated PI controller, carry out No Flow tuning before setting the PI controller parameters!
Low speed detection:
Low Speed Detection gives a signal if the motor is operating with minimum speed as set in 4-11 Motor Speed Low Limit [RPM]
or 4-12 Motor Speed Low Limit [Hz]. Actions are common with No Flow Detection (individual selection not possible).
The use of Low Speed Detection is not limited to systems with a no flow situation, but can be used in any system where
operation at minimum speed allows for a stop of the motor until the load calls for a speed higher than minimum speed,
e.g. systems with fans and compressors.
NOTE
In pump systems ensure that the minimum speed in 4-11 Motor Speed Low Limit [RPM] or 4-12 Motor Speed Low Limit [Hz]
has been set high enough for detection as the pump can run with a rather high speed even with valves closed.
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VLT HVAC Drive Programming Guide
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MG.11.CC.02 - VLT is a registered Danfoss trademark
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