Johnson Controls SABROE Unisab III Control, Engineering Manual

Page: 152 / 348

Engineering manual - UniSAB III 1.10.8
152/346
001930 en 2021.06
Compressor control and surveillance
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 algorithm.
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 opti-
mum 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 compressor is operating.
For SAB 202 S and SAB 202 L, which have automatic zero point setting, manual setting is usually 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 opti-
mum (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.