Alarm Latching - Lakeshore 335 User Manual

5.7.1.2 Alarm Latching

Latching Alarms: often used to detect faults in a system or experiment that
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requires operator intervention. The alarm state remains visible to the operator
for diagnostics even if the alarm condition is removed. Relays often signal remote
monitors, or for added safety take critical equipment off line. Latched alarms can
be cleared by pressing Alarm and selecting Yes to the Reset Alarm prompt. Select
No to the Reset Alarm prompt to enter the Alarm Setup menu.
Non-Latching Alarms: often tied to relay operation to control part of a system or
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experiment. The alarm state follows the reading value. The dead band parameter
can prevent relays from turning on and off repeatedly when the sensor input
reading is near an alarm setpoint.
FIGURE 5-6 illustrates the interaction between alarm setpoint and dead band in non-
latching operation. With the high alarm setpoint at 100 K and the dead band at 5 K,
the high alarm triggers when sensor input temperature increases to 100 K, and it will
not deactivate until temperature drops to 95 K. In addition, the same 5 K dead band is
applied to the low alarm setpoint as well.
High alarm activated
High alarm setpoint
Temperature reading
Alarm latching off
Deadband = 5 K
Low alarm setpoint
Low alarm activated
To setup an alarm, enter the Alarm Setup menu by pressing Alarm. If a latching alarm
has been activated, you will be prompted with a Reset Alarm? message. Select No to
enter the Alarm Setup menu.
Menu Navigation:
AlarmQInput (A, B)QAlarm (On)
AlarmQInput (A, B)QAlarm (On)
Low and High Setpoint limits are determined by the Preferred Units of the associated
sensor input.
Default:
LatchingQOff
DeadbandQ1.0000 K
Interface Command: ALARM
FIGURE 5-6 Dead band example
QLatching (Off, On)
ENTER
QDeadband (see note below)
ENTER
5.7.1 Alarms
High alarm deactivated
100 K
95 K
55 K
50 K
Low alarm deactivated
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