Grasso
Refrigeration Division
GRASSO SYSTEM CONTROL
Chap. 2 - 16 638660E_chapter2.doc
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2.7.2.5
Low suction pressure limitation
The suction pressure limitation attempts to prevent a low suction pressure alarm.
If the suction pressure reaches the initial limitation value, the compressor capacity cannot be increased any
further. If the suction pressure reaches the decrease limit, the compressor capacity is reduced by 1 capacity step
immediately.
The signal dominates compared to the capacity control and is effective until the suction pressure has become
less than the limit value and the limit timer has expired.
The suction pressure limitation function is illustrated in the following diagram.
P
suc
Suction pressure
A.. Time characteristic of the suction
pressure
V..
Forced reduction of the capacity due
too low suction pressure
B..
Low suction pressure limitation active
T..
Limit timer active; After that this
timer has expired the capacity control
is enabled again and the compressor
capacity can be increased.
b..
Limit value for disabling capacity
increase
f..
Limit value for forced reduction of
capacity
W.. Warning limit
Al.. Alarm limit
Figure 2.20, Low suction pressure limitation
Psuc low alarm
Low limit
+
Decr limit
+
Psuc low alarm:
Alarm limit for minimum suction pressure in bar (a)
Low limit:
Begin of the suction pressure limitation —
enter value as an offset to the alarm limit in bar
<<
Limit values 01
>>
Decr limit:
Begin of the forced capacity reduction —
enter value as an offset to the alarm limit in bar
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