74 34980A User’s Guide
2 Features and Functions
Using the Alarm Output Lines
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 assign an
alarm to any configured channel and multiple channels can be assigned to
the same alarm number. Each alarm output line represents the logical
“OR” of all channels assigned to that alarm number (an alarm on any of
the associated channels will pulse the line).
You can configure the behavior of the alarm output lines as described
below. The behavior of the alarm annunciators on the front panel also
tracks the alarm output configuration. The configuration that you select
is used for all four alarm output lines. A Factory Reset (
*RST command)
clears all four alarm outputs but does not clear the alarm queue in
either configuration.
• Latch Mode: In this mode, the corresponding output line is latched true
when the first alarm occurs and remains asserted until you clear it by
initiating a new scan or cycling power. You can manually clear the
output lines at any time (even during a scan) and the alarm data in
memory is not cleared (however, data is cleared when you initiate a
new scan).
• Track Mode: In this mode, the corresponding output line is asserted
only when a reading crosses a limit and remains outside the limit.
When a reading returns to within limits, the output line is
automatically cleared. You can manually clear the output lines at any
time
(even during a scan) and the alarm data in memory is not cleared
(however, data is cleared when you initiate a new scan). The alarm
outputs are also cleared when you initiate a new scan.
Alarms connector (as viewed from rear of instrument)
Alarm 4 Output (Pin 4)
Alarm 3 Output (Pin 3)
Alarm 2 Output (Pin 2)
Alarm 1 Output (Pin 1)
or
Gnd (Pin 9)
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