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88 L4400 User’s Guide
3 Operating and Programming
Using the Alarm Output Lines
As mentioned, there are two TTL alarm lines available on the rear-panel
Alarms connector. 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). The connector is shown below:
Figure 3-15. The L4400 Series Rear Panel Alarm Connector.
You can configure the behavior of the alarm output lines as follows. The
configuration that you select is used for both alarm output lines. A Factory
Reset (
*RST command) clears the 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.
• You can control the slope of the pulse from the alarm outputs (the selected
configuration is used for both outputs). In the falling edge mode, 0V (TTL
low) indicates an alarm. In the rising edge mode, +5V (TTL high) indicates
an alarm. A Factory Reset (
*RST command) will reset the slope to falling
edge.
Note: Changing the slope of the output lines may cause the lines to change
state.
5
1
9
6
Alarm 1 output (pin 1)
Alarm 2 output (pin 2)
Gnd (pin 9)
or