If the network pressure exceeds the TARGET value:
Outside the frequency converter's range of control the machine reverts to the selected control
mode.
DUAL:
The minimum controllable speed is reached and the machine switches to IDLE. The drive motor
runs unloaded with low power consumption.
When the preset idling time has elapsed, the machine switches to READY.
VARIO/QUADRO/CONTINUOUS:
The minimum controllable speed is reached and, depending on the air demand at the time, the ma‐
chine switches either to READY or to IDLE.
DYNAMIC:
The minimum controllable speed is reached and, depending on the air temperature of the drive mo‐
tor, the machine switches either to READY or to IDLE.
If the network pressure falls below the TARGET value:
The frequency converter runs the motor up to a speed at which air delivery matches the air de‐
mand.
The inlet valve opens and the machine delivers compressed air.
The frequency converter varies the speed of the drive motor according to the air demand. The
power consumption of the drive motor rises and falls according to air demand.
4.7.4 MODULATING control
With the help of a mechanical control valve (the proportional controller), the opening and closing of
the inlet valve is continuously varied in relation to the actual air demand. The airend delivers com‐
pressed air to the distribution network.
The load and power consumption of the drive motor rises and falls with the air demand.
To ensure optimal control on large compressors, the control air for the proportional controller is tak‐
en from an external air receiver.
4 Design and Function
4.7 Operating modes and control modes
9_9450 03USE
Service manual Controller
SIGMA CONTROL 2 SCREW FLUID 1.1.3
33
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