User`s guide

Features and Functions 3
Agilent 34980A Mainframe User’s Guide 133
• 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.
• Four TTL alarm outputs are available on the rear- panel Alarms
connector. You can use these hardware outputs to trigger external alarm
lights, sirens, or send a TTL pulse to your control system. 
You can also initiate a scan sweep (no external wiring required) when
an alarm event is logged on a channel. For complete details, refer to
“Using the Alarm Output Lines” on page 136.
Upper Limit
Lower Limit
Alarm Event No Alarm