Features and Functions 3
Keysight 34980A Mainframe User’s Guide 175
– When an alarm occurs, the instrument stores relevant information about the
alarm in the queue. This includes the reading that caused the alarm, the time
of day and date of the alarm, and the channel number on which the alarm
occurred. The information stored in the alarm queue is always in absolute time
format and is not affected by the FORMat:READing:TIME:TYPE command
setting.
– You must configure the channel (function, transducer type, etc.) before setting
any alarm limits. If you change the measurement configuration, alarms are
turned off and the limit values are cleared. Alarms are also turned off when you
change the temperature probe type, temperature units, or disable the internal
DMM.
– If you plan to use alarms on a channel which will also use Mx+B scaling, be
sure to configure the scaling values first. If you attempt to assign the alarm
limits first, the instrument will turn off alarms and clear the limit values when
you enable scaling on that channel. If you specify a custom measurement label
with scaling, it is automatically used when alarms are logged on that channel.
– If you redefine the scan list, alarms are no longer evaluated on those channels
(during a scan) but the limit values are not cleared. If you decide to add a
channel back to the scan list (without changing the function), the original limit
values are restored and alarms are turned back on. This makes it easy to
temporarily remove a channel from the scan list without entering the alarm
values again.
– Each time you start a new scan, the instrument clears all readings (including
alarm data) stored in reading memory from the previous scan. Therefore, the
contents of reading memory are always from the most recent scan.
– As shown below, alarms are logged in the alarm queue only when a reading
crosses a limit, not while it remains outside the limit and not when it returns to
within limits.
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