Agilent Technologies L4400 - Manual (Page 97)

Operating and Programming 3
L4400 User’s Guide 85
• If an alarm event occurs on a channel as it is being scanned, then
that channel’s alarm status is stored in instrument memory as the
readings are taken. Each reading that is outside the specified alarm
limits is logged in memory. You can store at least 500,000 readings in
memory during a scan. You can read the contents of instrument
memory at any time, even during a scan. Instrument memory is not
cleared when you read it.
• As alarm events are generated, they are also logged in an alarm
queue, which is separate from instrument memory. This is the only
place where non- scanned alarms get logged (alarms generated by the
digital modules). Up to 20 alarms can be logged in the alarm queue. If
more than 20 alarm events are generated, they will be lost (only the
first 20 alarms are saved). Even if the alarm queue is full, the alarm
status is still stored in reading memory during a scan. The alarm
queue is cleared by the
*CLS (clear status) command, when power is
cycled, and by reading all of the entries. A Factory Reset ( *RST
command) or instrument preset (SYSTem:PREset) does not clear the
alarm queue.
• You can assign an alarm to any configured channel and multiple
channels can be assigned to the same alarm number. However, you
cannot assign alarms on a specific channel to more than one alarm
number.
• 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 before setting any alarm limits. If you
change the measurement configuration, alarms are turned off and the
limit values are cleared.
• If you plan to use scaling on a channel which will also use Mx+B
scaling (L4450A counter function), 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.