14.SUCTION CONTROLS
Example
: Linear control linked with digital outputs from compressors with unloaders
On/Off compressors with unloaders.
In the compressors that use the unloader capacity regulation valve, the logic for actuating and shutting down the main relays and auxiliary unloader
valves is chosen according to parameters
1.2.x.34
- Sequence of actuations and
1.2.x.35
- Sequencing of shutdowns.
1.2.x.1
Control mode: Linear
1.2.x.2
Setpoint: 25 psi
1.2.x.4
On / Off Hysteresis: 6 psi
1.2.x.15
Number of compressors: 3
1.2.x.22
Compressor 1 modulation: ON / OFF
Compressor 1 is of the ON / OFF type and requires only one digital output connected to it. Compressor 2 has an unloader valve, so it is connected to two
digital outputs (main and auxiliary 1). Compressor 3 has two unloader valves, so it is connected to three digital outputs (main, auxiliary 1 and auxiliary 2).
The total number of digital outputs is six and its step is defined as: 6/6 = 1 psi.
.
14.4.1.2 Linear Mode associated with a VCC compressor in conjunction with ON / OFF compressors:
When the VCC compressor, analog or digital, operates together with On / Off compressors - with or without unloaders - the control is done through a
setpoint value and two hysteresis. The hysteresis of the VCC compressor (
1.2.x.5
) corresponds to the pressure range for controlling the output of
compressor 1 and the hysteresis of the On / Off compressors (
1.2.x.4
) corresponds to the control range of the other compressors.
The VCC compressor is the first to be actuated and the last to be shutdown. There is a validation time (
1.1.x.68
) for starting or stopping
compressors or unloaders valves when the compressor reaches its upper or lower limit of actuation. For each compressor or unloader actuated or
shutdown , the capacity of the VCC compressor is recalculated to compensate for the portion added or removed.
Example:
1.2.x.1
Control mode: Linear
1.2.x.2
Setpoint: 25 psi
1.2.x.4
Hysteresis On/Off: 4psi
1.2.x.5
VCC hysteresis: 2psi
1.2.x.9
Integral time: Off
Compressor 1 (proportional) uses analog output (0-10V), compressors 2 and 3 each use a digital output. The step of the digital outputs is defined as: 4/2
= 2 psi.
25
26
27
28
29
30
31
(psi)
Pc1
Pc1 + Pc2
Pc1 + Pc2 + Pc3
Pc1 + Pc2 + Pc3 + U1c2
Pc1 + Pc2 + Pc3 + U1c2 + U1c3
Pc1 + Pc2 + Pc3 + U1c2 + U1c3 + U2c3
OFF
Outputs
Pc1 = Compressor 1 main output
Pc2 = Compressor 2 main output
Pc3 = Compressor 3 main output
U1c2 = Auxiliary output 1 of compressor 2
U1c3 = Auxiliary output 1 of compressor 3
U2c3 = Auxiliary output 2 of compressor 3
1.2.x.23
Compressor 2 modulation: On / Off 50 I 100
1.2.x.24
Compressor 3 modulation: On / Off 33 I 66 I 100
1.2.x.28
Compressor 2 activation mode: Incremental
1.2.x.29
Compressor 3 activation mode: Incremental
1.2.x.34
Activation sequence: PPuu
1.2.x.35
Deactivation sequence: PPuu
1.2.x.15
Number of compressors: 3
1.2.x.22
Compressor 1 modulation: VCC-Analog
1.2.x.23
Compressor 2 modulation = On/Off
1.2.x.24
Compressor 3 modulation = On/Off
-Suction pressure
-VCC compressor capacity
-Compressor 2 main output
-Compressor 3 main ouput
Pc1
Pc2
Pc3
(psi)
Pc1 = 0% -> 100%
Pc1 = 0% -> 100%
Pc2
Pc1 = 0%
Pc1 = 100%
Pc2 + Pc3
Pc1 = 100% -> 0%
Pc2 + Pc3
Pc1 = 100% -> 0%
Pc2
Pc1 = 0%
25
27
29
31
psi
23
