20
Activation step = Hysteresis of digital outputs / Number of compressors = 12.0 / 3 = 4.0 psi
Disregarding the dead band effect, the pressure values for the activation of compressors 1, 2 and 3 would be 34.0, 38.0 and 42.0 psi, respectively.
Considering the dead band effect, no compressor must be activated until the pressure exceeds 45.0 psi, so compressors 1 to 3 will only be activated
when the pressure exceeds this value.
If the pressure decreases and enters the dead band region, the compressors will remain activated until the pressure exceeds the Lower dead band
differential interval. One compressor will be deactivated immediately and the others will be switched off gradually, respecting the time between
deactivations.
If the pressure drops rapidly and crosses the instant deactivation ranges, the compressor will be deactivated immediately.
Instant deactivation step = Lower dead band differential / (number of active stages - 1) = 10 / (3-1) = 5.
Compressor 3 will be deactivated upon crossing the lower limit, 20 psi, and compressors 1 and 2 will be deactivated as follows:
Case 1:
If the pressure remains within the range from 20.0 to 15.0 psi: Compressor 2 will be switched off 60 seconds after compressor 3 and compressor
1 will be switched off 60 seconds after compressor 2.
Case 2
: If the pressure drops rapidly to the range between 15.0 and 10.0 psi: Compressors 2 and 3 will be switched off immediately and compressor 1
will be switched off 60 seconds later.
Case 3:
If the pressure drops rapidly to less than 10.0 psi, all compressors will be switched off immediately.
14.4.4 Dead Band Mode with rotation:
The dead band control mode is applied in conjunction with the rotation, which gives preference for activating compressors with less operating time and
deactivating compressors with more operating time.
14.SUCTION CONTROLS
0
0
0
1
2
3
2
1
0
1
0
0
Case 1
Case 2
Case 3
10
15
20
30
34
38
45
42
Setpoint
Upper Dead
Band Differential
Lower Dead Band
Differential
Step of
compressor 3
Step of
compressor 2
Step of
compressor 1
Instant switch off
point 1
Instant switch off
point 2
Not activated at points
defined by the hysteresis
0
0
60s
Time between
deactivations
30s
Time between
activations
Number of compressors
connected
0 1 2 3
3
3
3
