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Appendix B Digitizer Basics
NI 5911 User Manual B-10 ni.com
Figure B-8. Difficult Pulse Train Signal
Ideally, the trigger event should occur at condition one, but sometimes
the instrument may trigger on condition two because the signal crosses
the triggerlevel. You cansolve thisproblem without using complicated
signal processing techniques by using trigger hold-off, which lets you
specify a time from the trigger event to ignore additional triggers that
fall within that time. With an appropriate hold-off value, the waveform
in Figure B-8 can be properly captured by discarding conditions two
and four.
• Input coupling—You can configure the input channels on your
NI 5911 to be DC coupled or AC coupled. DC coupling allows DC
and low-frequency components of a signal to pass through without
attenuation. In contrast, AC coupling removes DC offsets and
attenuates low frequency components of a signal. This feature can
be exploited to zoom in on AC signals with large DC offsets, such
as switching noise on a 12 V power supply. Refer to Appendix A,
Specifications, for input limits that must be observed regardless of
coupling.
5V
+V
t
Hold-off Hold-off
12 34
1 and 3 = Trigger Accepted
2 and 4 = Trigger Ignored
Trigger Level