Page 15
Device manual
6490B / 6490B-y / 6590B
W. Bälz & Sohn GmbH & Co. Koepffstraße 5 D-74076 Heilbronn Telefon (07131) 1500-0 Telefax (07131) 1500-21
3.7 Basic alarm type description
The controller has got three basic types of alarms called type A, type B and type C.
3.7a Alarm type A
Alarm at a limit value based on the setpoint SP.
Alarm at over-temperature if alarm setting
A1.A
is
positive. Alarm at under-temperature if alarm setting
A1.A
is negative. At positive setting the alarm is
triggered if PV is bigger than SP +
A1.A
. At
negative setting the alarm is triggered if PV is smaller
than SP -
A1.A
. The algebraic sign of the alarm
value
A1.A
only indicates the direction of effect
(over- or under-temperature).
The hysteresis defines a span between alarm state and
switching back to normal state. At positive setting of
A1.A
returning to normal state is at
SP +
A1.A
-
HY.1
. At negative setting of
A1.A
returning to normal state is at SP -
A1.A
+
HY.1
.
Alarm type A
3.7b Alarm type B
Alarm at a fixed limit value of PV.
If
AL.1
= 2, alarm is triggered if the value set at
A1.b
is reached or exceeded.
The hysteresis defines a span between alarm state
and switching back to normal state. Returning to
normal state is at
A1.b
-
HY.1
.
If
AL.1
= 4, alarm is triggered if the value set at
A1.b
is reached or dropped below.
The hysteresis defines a span between alarm state
and switching back to normal state. Returning to
normal state is at
A1.b
+
HY.1
.
Alarm type B
3.7c Alarm type C
Alarm at leaving a band around the setpoint SP.
The lower half of the band is defined by
A1.C
,
the higher one by
A1.C.
.
The value entered at
A1.C
is always negative
because the process variable PV has to be
smaller than SP -
A1.C
to trigger the alarm.
The value entered at
A1.C.
is always positive
because the process variable PV has to be
bigger than SP +
A1.C.
to trigger the alarm.
The hysteresis defines a span between alarm
state and switching back to normal state. For the
lower band returning to normal state is at
SP -
A1.C
+
HY.1
. For the higher band
returning to normal state is at
SP +
A1.C.
-
HY.1.
.
Alarm type C
At all three types (A, B, C) alarm is always triggered in case of sensor failure.
