Capacity Control With User Input 1 - Johnson Controls SABROE UniSAB III Engineering Manual

Compressor control and surveillance
3.1.12

Capacity control with user input 1

UniSAB III must be set in Remote mode in the picture Setup/Compr. Control. Select Setup/Configura-
tion/External input, and choose capacity set point control.
Ex.: The set point of the capacity slide on a screw compressor is to vary from 0 to 100% corresponding
to a change in the current signal from 4-20 mA.
Move the cursor to 4 mA, press
the cursor to 20 mA, press
the capacity can always be increased to 100%). Move the cursor to the second line, press
Capacity SP with or . Finish by pressing
The capacity slide will now move from 0% to 100% corresponding to a change in the current from 4-20
mA.
The capacity on a reciprocating compressor can be controlled the same way. The reciprocating com-
pressor changes one capacity stage up or down depending on whether the signal is above or below the
percentage corresponding to the capacity stage in question. The timers Delay up and Delay down,
which are used during the loading/unloading of capacity stages, are also active when capacity regulation
takes place with an external 4-20 mA signal.
This means that for an SMC 108 without total unloading the following changes apply:
0% < = Signal
25% < = Signal
50% < = Signal
75% < = Signal
100% < = Signal
This works as follows:
Start
When the signal is above 5% (4.8 mA) and Auto start = Yes has been configured, the timer Delay before
start will begin to count down (screw compressors).
For reciprocating compressors, the timer Delay before start will start once the signal is above the lowest
capacity stage. When the timer Delay before start has counted down, the compressor will start and fol-
low the signal up/down. Note, however, that various limiters may reduce the compressor capacity.
Stop
When the signal is below 5% (4.8 mA) and Auto stop = Yes has been configured, the timer Delay before
stop will begin counting down (screw compressors). For reciprocating compressors, the timer Delay be-
fore stop will start once the signal is below the lowest capacity stage. For reciprocating compressors with
total unloading, the timer Delay before stop will be activated when the signal is below 0%. When the De-
lay before stop timer has finished counting down, the compressor will stop.
If the current signal drops to -10% (2.4 mA), the chosen form of regulation will change (e.g. suction pres-
sure regulation, brine regulation, etc). If the signal exceeds -10% once more, regulation will change back
to capacity remote control. When UniSAB III is configured to capacity set point, the start number
Engineering manual - UniSAB III 1.10.8
001930 en 2021.06
and change the value to 0 (skip this if the value is already 0). Move
and change the value 100. (The value can be set to 102 to make sure that
. The picture will now look like this:
< 25% = 0% capacity
< 50% = 25% capacity
< 75% = 50% capacity
< 100% = 75% capacity
= 100% capacity
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and select