Version 2.02 15.05.2007 Function of VS 3000
10
Compressors that can be allocated to the speed adjuster by base load rotation are the first to be cut out. Load-
ing and unloading of fixed-speed compressors also depends on the compressor type. If the compressor pack is
operated with capacity-controlled compressors, the load and unload points for the fixed-speed compressors will
be different.
With capacity-controlled compressors the auxiliary capacity stage is used only for the variable speed com -
pressor. The fixed-speed compressors are always operated at 100% capacity, meaning that the base and ca-
pacity stages of these compressors are always loaded and unloaded simultaneously. The graph below shows
the controller action for a pack of two non-capacity-controlled compressors.
Compressor without capacity control
- Single stage compressor -
Frequency of speed-controlled
compressor [Hz]
Relative refrigeration capacity of compressor [%]
ZNR. 51203 64 330 E0
The next graph shows the controller action for a pack of two compressors equipped with two-stage capacity control.
ZNR. 51203 64 430 E0
Relative refrigeration capacity of compressor [%]
Compressor with capacity control
- Two-stage capacity control -
Frequency of speed-controlled
compressor [Hz]
This requires the characteristic of the frequency changer to be definable for an output signal of 0 V at the analog
output for compressor control to correspond to a frequency of 25 Hz and an output signal of 10 V to correspond
to a frequency of 87 Hz.
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