HP 54750A, User Manual, Page: 236 / 478

Increasing Measurement Accurac y
and Time-Interval Measurement
Increasing Measurement Accuracy
A utomatic measurements
Except in special cases , the simplest and most accurate way to measure the
width of a pulse is to use the instrument's automatic measurement.
F or the instrument to measure the pulse width automatically , the
time/division control must be set so that the entire pulse , including the
leading and trailing edges , is on the screen. Thus , the resolution of the
measurement is limited by the time base resolution. In digitizing scopes ,
the time base resolution is primarily limited by memory depth and by the
intrinsic hardware resolution of the ne interpolator in the time base .
It is important to select the optimum time/division scale to achieve the best
resolution and accuracy . Both edges of the pulse must be on the screen, and
at the same time , there must be sucient baseline (or top for a negative
pulse) for the top and base algorithm to reliably determine the voltage level
of the base (or top). Refer to the discussion in \Calculating top and base" in
Chapter 7, describing the algorithm the instrument uses to determine the top
and base levels .
If the baseline is distorted prior to the initial transition of the pulse , enough of
the \true" steady-state baseline must be present on the screen so that it will
be identied clearly in a voltage histogram as the most prevalent value . The
minimum time/division setting that achieves this will give the most accurate
measurement. In other words , spread the pulse out to occupy as much of the
screen as possible while allowing the base (or top for a negative pulse) to
occupy at least 10 percent of the display (1 division).
The instrument allows you to select time/division settings other than the
standard 1-2-5 sequence . F or example , consider a pulse that is 5.8 s wide .
At 1 s/division, the pulse will be 5.8 divisions wide , or 58 percent of the
screen width. However , at 500 ns/div , the leading and trailing edges will
not be on the screen simultaneously . Here , you could set the time base to
650 ns/division, and the pulse will occupy 90 percent of the screen.
The instrument has automatic measurements for all common pulse
parameters . Y ou can congure the Delay automatic measurement to measure
any arbitrary time interval. Use the Dene Measure menu to specify which
interval the Delay automatic measurement will measure . Y ou can store
several custom delay measurement congurations using the Setup menu.
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