Chapter 11
Triggering
X Series User Manual
11-8
ni.com
Analog Trigger Accuracy
The analog trigger circ
u
itry compares the voltage of the trigger so
u
rce to
the o
u
tp
u
t of programmable trigger DACs. When yo
u
config
u
re the level
(or the high and low limits in window trigger mode), the device adj
u
sts the
o
u
tp
u
t of the trigger DACs. Refer to the specifications doc
u
ment for yo
u
r
device to find the acc
u
racy or resol
u
tion of these DACs, which also shows
the acc
u
racy or resol
u
tion of analog triggers.
To improve acc
u
racy, do the following:
•
Use an AI channel (with a small inp
u
t range) instead of APFI <0,1> as
yo
u
r trigger so
u
rce. The DAQ device does not amplify the
APFI <0, 1> signals. When
u
sing an AI channel, the NI-PGIA
amplifies the AI channel signal before driving the analog trigger
circ
u
itry. If yo
u
config
u
re the AI channel to have a small inp
u
t range,
yo
u
can trigger on very small voltage changes in the inp
u
t signal.
•
Software-calibrate the analog trigger circ
u
itry. The propagation delay
from when a valid trigger condition is met to when the analog trigger
circ
u
itry emits the Analog Comparison Event may have an impact on
yo
u
r meas
u
rements if the trigger signal has a high slew rate. If yo
u
find
these conditions have a noticeable impact on yo
u
r meas
u
rements, yo
u
can perform software calibration on the analog trigger circ
u
itry by
config
u
ring yo
u
r task as normal and applying a known signal for yo
u
r
analog trigger. Comparing the observed res
u
lts against the expected
res
u
lts, yo
u
can calc
u
late the necessary offsets to apply in software to
fine-t
u
ne the desired triggering behavior.
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
