HP 54620A, User'S And Service Manual

Page: 136 / 243

In the previous figure, the trigger point is off-screen to the left—that is why
the solid triangle is at the left edge of the graticule. If you now pan the
display back by setting the delay to 20
µ
s, the result looks like the following:
Panning the Display to View the Start of Acquisition
Note that the trigger point (the solid triangle at the top of the graticule),
while visible on-screen, occurs sometime before the first acquisition in
memory. Also, you must be careful when interpreting the time reference
point here—panning the display with no acquisition in process is simply
panning the display—it does not change the reference point. If you start a
new acquisition after stopping and panning, the delay value to which you
panned will be used in determining the trigger location for the new
acquisition. For example, if you acquired data with a delay value of 100
µ
s,
then stop and pan the display to 50
µ
s, the new acquisition will position the
trigger 50
µ
s before the time reference point. Panning is a useful way to see
the relationship between the trigger point and relative locations in acquisition
memory.
Here is the trigger
point
The first location in
acquisition memory
does not occur until
here
The memory bar shows
that most of acquisition
memory is off-screen to
the right
Figure 39
Ensuring Accurate Measurements
Time base and Acquisition
135