pressure or too low oil pressure. The start-up limiter can maximum be active for the time set
in timer Max. start-up time, which default is set to 600 sec.
When the Max. start-up time timer is running the Start-up limiter is an alarm. When the Max.
start-up time timer runs out the Start-up limiter alarm is converted into a shutdown and the
compressor is stopped.
2.2.22 Start up RPM limiter
High pressure compressors (SAB 157HR)
The alarm indicates that the speed is limited to minimum speed, default 1,000 [rpm] during
start-up because of too high suction pressure.
The start-up limiter can maximum be active for the time set in timer Start RPM limiter (de-
fault 300 seconds). When the limiter is active the Start RPM limiter timer is running and a
Start-up RPM limiter alarm is shown. If the Start RPM limiter timer runs out while the limiter
is still active the compressor is stopped by a shutdown Start RPM limiter error.
2.2.23 Lube pressure unload alarm
High pressure compressors (SAB 157HR)
This alarm indicates that the oil lubricating pressure is low and that the plug valve therefore
has been unloaded. See Fig. 7.
2.2.24 No communication to chiller
The shutdown/alarm will only be activated if Unisab III is configured as part of a chiller con-
trol, i.e. Configuration/plant/ Chiller = Yes.
The shutdown will only be activated if the communication between Unisab III and the connec-
ted chiller disappears for a longer period than the one set in the No chiller timer.
2.2.25 Chiller, shutdown from chiller
The shutdown will only be activated if Unisab III is configured as part of a chiller control, i.e.
Configuration/plant/Chiller = Yes. The shutdown will be activated if the shutdown of the con-
nected chiller goes off.
2.2.26 Watch the oil pressure
The alarm will be activated if the oil pump for oil charging is started by means of the picture
Timers/Oil charging and the compressor is in operation at the same time.
2.2.27 Vi position error
The shutdown will only be activated if Unisab III is configured for automatic Vi regulation, i.e.
Volume ratio is set to Auto in picture Configuration/compressor block. The shutdown indicates
that the shown capacity in connection with automatic Vi regulation is incorrect. The real ca-
pacity of the compressor is lower than the one shown in the display.
2.2.28 Low lubricating pressure monitoring (screw compressor)
The reason for this shutdown is that the differential pressure across the compressor and thus
the effective lubricating pressure are too low. The differential pressure is calculated the fol-
lowing way: Absolute oil pressure - 1.1 x Absolute suction pressure.
The differential pressure must be higher than the set shutdown limit for low oil pressure, see
Fig. 7.
An alarm will be issued after 25 seconds and a shutdown after 120 seconds.
Alarms and shutdowns
Engineering manual - Unisab III 1.10
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