Version 2.02 15.05.2007
Function of VS 3000
7
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3.2.4 Control algorithm with step controller
Low pressure as detected by an A/D converter is compared with the setpoint:
Control error = Actual value (t
0_Act
) − setpoint (t
0_Setp
)
With small control errors the pressure change within the controller cycle time is also evaluated. When the control
error is positive and the pressure is greater than the setpoint plus 1.5 times the neutral zone, the step switch
moves one step up regardless of pressure change.
As a result the compressor having the shortest run time is enabled. If the control error is positive, pressure is
falling and is less than the setpoint plus 1.5 times the neutral zone, no compressor actuation takes place in the
expectation that the neutral zone will be reached shortly.
When the control error is negative and the pressure is lower than the s etpoint less the neutral zone, the step
switch moves one step down regardless of pressure change. As a result the compressor having the longest run
time is disabled. If the control error is negative, pressure is rising and is greater than the setpoint less the neutral
zone, no compressor actuation takes place.
No compressor actuation takes place when the control error is within a definable neutral zone.
Neutral zone (NZ)
t
Time
ZNR. 51203 64 030 E0
0
Suction pressure
t
0 Setp
- 1,0 NZ
t
0 Setp
-NZ0,5
t
0 Setp
+NZ0,5
t
0 Setp
+ 1,5 NZ
Step
up
No step Step
down
No step
t
0 Setp
VS 3000 control algorithm LP step controller
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