Tempco tec-220, Instruction Manual, Page: 17 / 36

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3.3 & 3.4 Alarm Figures
3–4 Alarm
Output 2 can be set as an alarm output. There are six types of
alarm functions and one dwell timer that can be selected, and
four kinds of alarm modes (ALMD) are available for each
alarm function.
A process alarm sets two absolute trigger levels. When the
process value is higher than SP2, a process high alarm
(PV.HI) occurs. The alarm is off when the process value is
lower than SP2-ALHY. When the process value is lower than
SP2, a process low alarm (PV.LO) occurs, and the alarm is
off when the process value is higher than SP2+ALHY. A
process alarm is independent of the set point.
A deviation alarm alerts the user when the process value
deviates too far from the set point. When the process value is
higher than SV+SP2, a deviation high alarm (DE.HI) occurs,
and the alarm is off when the process value is lower than
SV+SP2-ALHY. When the process value is lower than
SV+SP2, a deviation low alarm (DE.LO) occurs, and the
alarm is off when the process value is higher than
SV+SP2+ALHY. The trigger level of the deviation alarm
moves with the set point.
A deviation band alarm presets two trigger levels relative
to the set point. The two trigger levels are SV+SP2 and SV-
SP2 for alarm. When the process value is higher than
(SV+SP2) or lower than (SV-SP2), a deviation band high
alarm (DB.HI) occurs. When the process value is within the
trigger levels, a deviation band low alarm (DB.LO) occurs.
There are four types of alarm modes available for each alarm
function. These are: normal alarm, latching alarm, holding
alarm and latching/holding alarm. They are described as fol-
lows:
Normal alarm: ALMD=NORM
When a normal alarm is selected, the alarm output is de-ener-
gized in the non-alarm condition and energized in an alarm
condition.
Latching alarm: ALMD=LTCH
If a latching alarm is selected, once the alarm output is ener-
gized, it will remain unchanged even if the alarm condition
is cleared. The latching alarm is reset when the RESET key
is pressed after the alarm condition is removed.
Holding alarm: ALMD=HOLD
A holding alarm prevents an alarm when the control is pow-
ering up. The alarm is enabled only when the process reaches
the set point value. Afterwards, the alarm performs the same
function as a normal alarm.
Latching/holding alarm: ALMD=LT.HO
A latching/holding alarm performs both holding and latching
functions. The latching alarm is reset when the RESET key
is pressed after the alarm condition is removed.
Alarm failure transfer is activated as the unit enters failure
mode. The alarm will go on if ALFT is set for ON and go off
if ALFT is set for OFF. The unit will enter failure mode when
a sensor break occurs or if the A-D converter of the unit fails.