3
Features and Functions
174
Keysight 34980A Mainframe User’s Guide
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”
page 181.
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.
