User`s guide

132 Agilent 34980A Mainframe User’s Guide
3 Features and Functions
Alarm Limits
The instrument has four alarms which you can configure to alert you
when a reading exceeds specified limits on a channel during a scan. 
You can assign a high limit, a low limit, or both to any configured channel
in the scan list. You can assign multiple channels to any of the four
available alarms (numbered 1 through 4). For example, you can configure
the instrument to generate an alarm on the Alarm 1 output when a limit
is exceeded on any of channels 1003, 2025, or 3020.
You can also assign alarms to channels on the modules with digital I/O
capabilities (34950A and 34952A). For example, you can generate an alarm
when a specific bit pattern or bit pattern change is detected on a digital
input channel or when a specific count is reached on a totalizer channel.
With the digital modules, the channels do not have to be part of the scan
list to generate an alarm. For complete details, see “Using Alarms With the
Digital Modules” on page 138.
Alarm data can be stored in one of two locations depending on whether a
scan is running when the alarm occurs.
1 If an alarm event occurs on a channel as it is being scanned, then that
channel’s alarm status is stored in reading 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 reading memory at any time, even
during a scan. Reading memory is not cleared when you read it.
2 As alarm events are generated, they are also logged in an alarm queue,
which is separate from reading memory. This is the only place where
non- scanned alarms get logged (alarms during a monitor, alarms
generated by the digital modules, etc.). 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) 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.