This ensures that the oil pressure is raised quickly at compressor start-up. The compressor
will stay at this speed as long as the main oil pressure is low. The alarm Forced speed active
will be given as long as the speed is kept forced up. The forced speed regulation will not be
deactivated until the main oil pressure (P
oil
abs - P
suct
abs x 1.5) is above the defined mini-
mum limit of 1.0 bar. Speed is then reduced to motor rpm min. speed in manual operation or
it is set free and controlled by the capacity regulator in automatic operation.
11: Drive cap limit
90 to 100%
Enter the capacity slide limit where Unisab III starts to increase the drive speed. For SAB 120,
151, 157HR, 193, 233, 283 and 355 with frequency converter it is possible to adjust the ca-
pacity slide limit where Unisab III starts to increase the drive speed above motor rpm min.
The drive capacity limit can be set between 90 and 100%.
Do not change this limit unless you encounter problems with the capacity slide, which for
some reason prevents the slide from reaching a slide capacity at 98.0% (default value).
Please note that on compressors with both capacity slide and frequency converter the Actual
capacity value shown in the Unisab III info bar is the total capacity of the compressor for
which we use the term “yield”. The relation between yield and slide capacity is as follows:
Yield [%] = Slide capacity [%] * (motor speed / motor rpm max).
12: Rota Recip
Step (Applicable for Centa coupling and for Rexnord coupling – if resonance frequencies are
skipped)
Speed (Applicable only for Centa coupling)
Select the Step method to use the standard Rota control method for reciprocating compres-
sors. For some compressor types it is possible to set and operate with a low minimum rpm
value under part load. See subsection 3.4.6. Rota (VSD) for more information.
Select the Speed method to be used on reciprocating compressors equipped with VSD and
the soft Centa coupling. It is not recommended for reciprocating compressors equipped with
the standard Rexnord coupling, as it may lead to torsional vibration problems. For some com-
pressor types it is possible to set and operate with a low minimum rpm value under part load.
See subsection 3.4.6. Rota (VSD) for more information.
13: Motor rpm min. 2
500 to 1000 revolutions/minute - for SMC reciprocating compressors
700 to 1000 revolutions/minute - for CMO reciprocating compressors
Enter the minimum rpm 2 value which may be used in combination with the minimum rpm
value when running the Step or Speed configuration. When more than half of the steps are
engaged a higher minimum speed 2 is used. This higher minimum speed is necessary to
maintain proper motor fan cooling for standard motors at a higher load than 50%. See sub-
section 3.4.6. Rota (VSD) for more information.
For SMC/HPC/TSMC with frequency drive it is possible to set the minimum limit for Motor rpm
min 2 to 500 rpm. The default setting remains at 700 rpm.
For CMO/HPO/TCMO with frequency drive it is possible to set the minimum limit for Motor rpm
min 2 to 700 rpm. The default setting remains at 900 rpm.
Set-up
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Engineering manual - Unisab III 1.10
001930 en 2014.09
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