Determining The Sample Interval - Tektronix 11801C User Manual

Acquisition
Determining the
Sample Interval
3 2
A trace remains on the display until it is replaced by a more recent acquisi
tion or until you clear the trace. The process of clearing traces is described
on page 3 5.
You can set the number of points in a trace record, called the record length,
to be 512, 1024, 2048, 4096, or 5120 points. Setting the record length is
described in more detail on page 3 161.
The sample interval is the time difference represented between successive
points on the trace record. This is different from the sampling rate, which is
the actual time that it takes to sample and digitize the successive points in
the trace record. Since only one point is sampled and digitized after a trigger
event, the sampling rate is much slower than the sample interval.
To compute the sample interval, divide the time period that the trace record
displays by the number of points in the trace record. For example, if you are
display a trace at 20 ns per division, the trace displays a little more than
200 ns of time. (There are a few points outside the 10 division graticule on
either side.) If the trace has 2048 points, the sample interval is 200 ns di
vided by 2048, or 100 ps.
All traces on the main time base have the same record length and horizontal
size. Similarly, all traces on window time bases share the same record
length and horizontal size. This means that the 11801C uses one sample
interval for main traces and a different sample interval for window traces.
You can see what the current sample intervals are by looking at the top of
the Horizontal Desc pop up menu in the Waveform major menu.
Reference