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81901 “MSW_GPC-40/600A”_03-2021_ENG_page 138
4.4. Alarms
4.4.1.
Generic alarms AL1...AL8
Generic alarms
AL1
…
AL8
can be of 4 main types, shown
below:
Normal absolute alarm
(
AL
.1 inverse and absolute,
AL.2
direct and absolute).
Two alarm thresholds are set,
AL.1
(lower threshold) and
AL.2
(upper threshold), which correspond to two hysteresis
values,
Hy.1
(positive) and
Hy.2
(negative). The alarm is
triggered when the measured value remains below
AL.1
or
greater than
AL.2
for the set activation delay times.
The alarm condition stops when the measured value is
greater than
AL.1
+
Hy.1
, or is less than
AL.2
-
Hy.2
. This
avoids repeated alarms caused by slight variations in the
measured value.
Any alarm signal at startup, when the equipment is not in
normal operation, can be avoided by disabling it when pow-
er is turned on.
Symmetrical absolute alarm
A single
AL.1
alarm threshold and a single
Hy.1
hysteresis
value are set.
With the direct alarm setting, the alarm is triggered when
the measured value is less than
AL.1
-
Hy.1
or greater than
AL.1
+
Hy.1
for the set delay activation time.
With the inverse alarm setting, the alarm is triggered when
the measured value is greater than
AL.1
-
Hy.1
or less than
AL.1
+
Hy.1
for the set delay activation time.
Normal alarm for the reference variable
A single hysteresis value
Hy.2
(negative), an alarm threshold
AL.2
and the value to which it relates are set. The previous
alarm threshold (in this case
AL.1
) is used as the relative
value. With the direct alarm setting, the alarm is triggered
when the reference value (
A2.r
) is greater than
AL.1
+
AL.2
for the set delay activation time. The alarm condition stops
when the measured value is less than
AL.1
+
AL.2
-
Hy.1
.
With the reverse alarm setting, the alarm is triggered when
the measured value (
A2.r
) is less than
AL.1
+
AL.2
-
Hy.1
for
the set delay activation time. The alarm condition stops
when the measured value exceeds
AL.2
+
AL.1
.
Symmetrical alarm relative to the reference variable
A single hysteresis value
Hy.2
(negative), an alarm threshold
AL.2
and the value to which it relates are set. The previous
alarm threshold (in this case
AL.1
) is used as the relative
value.
With the direct alarm setting, the alarm is triggered when
the reference value (
A2.r)
is less than the value
AL.2
-
AL.1
,
or is greater than the value
AL.2
+
AL.1
.
With the reverse alarm setting, the alarm is triggered when
the measured value is between
AL2
-
AL.2
and
AL.2
+
AL.1
.
Normal absolute alarm
Symmetrical absolute alarm
Alarm relative to the reference variable
alarm 1
AL.2
AL.2 - Hy.2
AL.1 + Hy.1
AL.1 + Hy.1
AL.1 - Hy.1
Hy.2
Hy.2
Hy.2
AL.1
AL.1
AL.1
AL.1
AL.1+AL.2
AL.2+AL.1
AL.2-AL.1
alarm 2
time
time
time
time
Symmetrical alarm relative to variable
reverse
direct
reverse
direct
reverse
direct
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