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2640A/2645A NetDAQ
Users Manual
1-10
Master Alarm 1-13.
Master Alarm is an instrument output line that is logic low (nominal +0.8V dc)
for as long as any channel is in alarm while scanning is active. The connection
uses the ALARM/TRIGGER I/O terminals MA and GND (Figure 1-4). This TTL
output interfaces with external equipment such as warning lights, alarms,
automatic shutdowns, and paging systems. When the alarm condition ends or
scanning stops, an internal pull-up resistor sets the output at logic high (nominal
+5.0V dc).
Interval Trigger 1-14.
Interval Trigger triggers scanning at regular time intervals using Interval 1.
Interval 1 is in seconds, with a minimum of 0.000 (continuous scanning) and a
maximum of 86400.000 (one scan every 24 hours). The time resolution is to the
millisecond, for example, 12.345 seconds.
External Trigger 1-15.
External Trigger triggers scanning when an external logic low is applied to the
instrument TI (Trigger In) line. As long as the Trigger Input remains low, scans
are triggered at regular time intervals using Interval 2. Interval 2 is in seconds,
with a minimum of 0.000 (continuous scanning) and a maximum of 86400.000
(one scan every 24 hours). The time resolution is to the millisecond, for example,
12.345 seconds. When scanning starts, if the External Trigger is logic low,
scanning begins at the Interval 2 rate. If the External Trigger is logic high, no
scans are triggered until the trigger line is set to logic low.
You can combine External Trigger with Alarm Trigger and Interval Trigger. For
example, if the Interval Trigger is set for 60 seconds (Interval 1) and the External
Trigger is set for 10 seconds (Interval 2), scanning is at 60-second intervals except
when External Trigger is low, when scanning is at 10-second intervals.
If one or more external trigger events occur while a scan is in progress, one scan
triggers following the scan in progress.
Alarm Trigger 1-16.
Alarm Trigger triggers scanning when a channel designated as an alarm trigger
goes into alarm. As long as any such channel is in alarm, scans are triggered at
regular time intervals using Interval 2. Interval 2 is in seconds, with a minimum of
0.000 (continuous scanning) and a maximum of 86400.000 (one scan every 24
hours). The time resolution is to the millisecond, for example, 12.345 seconds.
The instrument performs background monitoring of channels designated as alarm
triggers to check for alarm conditions using Interval 3. (See “Configuring the
netdaq.ini File” in Chapter 3 of this manual.)