Automatic Setting Of New Zero Point (Sab 202); Manual Setting Of New Zero Point (All Screw Compressors); Built-In Spacer Block - Johnson Controls SABROE Unisab III Control Engineering Manual

Corrected capacity
Pressure cond.
1.5
Cap. slide
Measured slide pos.
0%
0%
The capacity slide signal from the position transmitter is scaled in such a way that 0% is read
when the slide position corresponds to the calculated/set zero point and 100% is read when
the capacity slide meets the Vi slide. It makes no difference whether the setting is carried out
automatically or manually.

3.8.3 Automatic setting of new zero point (SAB 202)

The zero point for the various types of SAB 202 is calculated according to a programmed al-
gorithm.
The current calculated value of the zero point is displayed in the picture Service/Diagnose/
Zero cap.pos.
With manual Vi regulation, the zero point is corrected and set automatically corresponding to
an optimum setting of the Vi slide. Consequently it is very important that the setting of the Vi
slide is correct.

3.8.4 Manual setting of new zero point (all screw compressors)

For all screw compressor types without automatic zero point setting, you can manually set a
"zero point" below which the compressor capacity slide is not allowed to drop while the com-
pressor is operating.
For SAB 202S and SAB 202L, which have automatic zero point setting, manual setting is usu-
ally not allowed.
The manual setting of the zero point is carried out in the picture Setup/Configuration/
Compressor Block in the configuration point: Manual zero 0.0%
The setting ranges between 0-40% of maximum capacity slide travel (at Vi ratio = 2).
With manual Vi regulation the zero point is corrected automatically by a factor that depends
on an optimum (calculated) setting of the Vi-slide. Consequently, it is very important that the
setting of the Vi slide is correct.
The setting will be stored when the compressor stops and/or Unisab III is switched off.

3.8.5 Built-in spacer block

If the compressor has a built-in spacer block and automatic Vi regulation, the mechanical zero
must be set to Yes. This will reduce the travel of the capacity slide by the percentage value
[0-40%] entered in Manual zero and the corrected capacity can be calculated and shown cor-
rectly.
The value [0-40%] that must be entered in Manual zero must have the following size:
0%
Volume cond.:
12 25
Zero % pos.
"Zero slide"
136/319
Compressor control and surveillance
100%
4.5 3 2
100%
100% 0%
"Vi slide"
Engineering manual - Unisab III 1.10
001930 en 2014.09