Chicago Pneumatic CPVS 20, Инструкция по эксплуатации, Страница: 18 / 28

Chicago Pneumatic Compressors
62 305 454 65
01/2008
Page 18
• Pressure control for low rates of flow
For an air consumption rate lower than the minimum rate of flow
for the machine, the pressure is adjusted by the machine's time-
delayed START/STOP controls.
Since the operation element cannot function below a certain speed
(corresponding to the minimum output), the compressor conti-
nues to run and compress at the minimum speed until the pres-
sure reaches the limit called "Indirect shutdown ".
Once this threshold has been reached, the motor will stop, the
machine will go into stand-by mode after a certain period of
inactivity and the full drainage process will be carried out.The
pressure then drops towards the indicated pressure and, at the
end of the minimum time delay (since reaching the no-load pres-
sure), the drive allows the motor to restart. The pressure then
rises again and the cycle starts over (
Fig. 9 d ).
To avoid pumping the system - frequent stop / start - drainage
time may be increased.
Fig. 9a
The principle of the pressure control by variable speed
• Energy saving
For demand of compressed air within the machine's flow range -
min flow to max flow, the frequency converter or the variable
speed drive feed the motor in order to ensure that it turns at the
speed required to supply air demand both for pressure and flow.
It is used to adjust the power supply to the motor (and thus the
machine) to the exact power requirement for the compression of
the air, without a drainage stage being necessary.
COMMENT :
Energy savings are increased if machine maintenance is carried
out in accordance with the maintenance instructions and frequency.
Controller Pressure
required
Drive
Motor Compressor
unit
Tank
System
Pressure sensor
Frequency speed
• The principle of the pressure control by changing the speed
The ES 3000 controller controls the motor and the compressor
as a function of the system pressure as measured by an internal
pressure sensor (
Fig. 9a ).
- If the mains pressure is weaker than the pressure set point
(user-defined parameter in the ES 3000 ) the motor will
accelerate and the pressure will increase ( Fig. 9b )
- If the mains pressure is stronger than the pressure set point, the
motor will slow down causing the pressure to drop.
The ES 3000 provides the compressor control functions and also
controls the whole pressure feedback loop. It therefore includes a
device to compare the indicated pressure with that from the pres-
sure sensor, associated with a compensating device, Proportional
integral control PI (
Fig. 9c ).
The drive, a result of the latest developments in power electronics,
is one of the smallest in size on the market, thanks to its use of
high cut-out frequencies with IGBT transistors.
At the same time, the motor control method known as "open loop
vector flux control " provides good stability for the system against
disruption.
In this way, the pressure feedback loop is more stable to sudden
changes in consumption (changes in the flow-rate).