GEA Grasso - Page 47

Grasso
Refri
g
eration Division
GRASSO SYSTEM CONTROL
01.2004/1 638660E_chapter2.doc Chap. 2 - 11
2.7.1 Oil system monitor of piston compressor packages
The oil system monitor is responsible for monitoring the functionality of the oil system. The package is switched
off if alarms occur.
The difference between the oil pressure and the crankcase pressure is monitored. In case no crankcase pressure
is measured, the suction pressure is used in stead.
2.7.1.1 Switching sequence in the normal case
Start conditions fulfilled
Unloaded start
Output — compressor motor on
’Oil dif press’ OK
’Oil dif start’ timer active
’Oil dif run’ timer active
’Low oil differential pressure’ alarm
Figure 2.13, Oil system monitor in the normal case
A.. During start up
B.. Brief lowering of the oil differential pressure during running
•
If
(1) Start conditions fulfilled
→
Then
(2) Set the actuating signal ’Unloaded start’
→
Then
(3) Output — compressor motor on
•
If
(3) Output — compressor motor on equals 1
→
Then
(5) Start ’Oil dif start’ timer
•
If
(4) ’Oil dif press’ OK equals 0
and
•
If
(5) ’Oil dif start’ timer expired
→
Then
(6) Start ’Oil dif run’ timer
If the oil differential pressure is OK again within the appropriate delay time, there is no alarm shutdown.