GEA Grasso, Руководство пользователя

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Grasso
Refrigeration Division
GRASSO SYSTEM CONTROL
Chap. 2 - 10 638660E_chapter2.doc
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2.7 Safety control (Alarms, warnings and limitations)
The following situations are taken into account for activating the alarm output signal:
•
Oil system alarms
•
Minimum / maximum limits reached
•
Compressor motor’s start equipment alarms
•
Hardware or sensor failures
•
Safety timers exceeded
The formation of a limit value signal is illustrated in the following diagram.
A.. Time characteristic of
process value
V.. Forced change of capacity
B.. Limitation active
T.. Limit timer active; After
that this timer has expired
the capacity control in the
direction in which the
limitation is active is
enabled again.
ML W.. Warning active
ML A.. Alarm active
AL.. Alarm limit of the process
value
+ Offset.. Positive or negative offset
- Offset
value for calculation of the
appropriate limit
W.. Warning limit of the process
value (= AL + Offset W)
b.. Limitation limit of the
process value for disabling
change of capacity in the
direction of the limitation
(=Al + Offset b)
f.. Limitation limit of the
process value for forced
change of capacity
(= AL + Offset f)
3.. Alarm reset
Figure 2.12, Example of the formation of a limit value signal
)
To prevent the compressor capacity to be changed in the direction of the limitation directly after that the
limitation has ended a limit timer is used. This timer ensures that during a minimum time no capacity
changes can be made in the direction for which the limitation was active. The timer restarts itself as long
as the limitation is active.