HP 1660CS, User Manual

Page: 218 / 347

Automatic measurement algorithms
The following explains top and base voltages, then defines the measurement
algorithms.
Top and base voltages
All measurements except Vp_p are calculated using the V
top
(100% voltage)
and V
base
(0% voltage) levels of the displayed waveform. The V
top
and V
base
levels are determined from an occurrence density histogram of the data
points displayed on the screen.
The digitizing oscilloscope displays 8-bit vertical voltage resolution. In other
words, the vertical axis of the display is divided into 2
8
voltage levels. Each
of these 256 levels is called a quantization level. Each waveform has at least
500 data points displayed on the horizontal axis of the screen. Each of these
data points has one quantization level assigned to it. The histogram is
calculated by adding the number of occurrences of each quantization level of
all displayed points on the displayed waveform.
The quantization level with the greatest number of occurrences in the top
half of the waveform corresponds to the V
top
level. The quantization level
with the greatest number of occurrences in the bottom half of the waveform
corresponds to the V
base
level.
If V
top
and V
base
do not contain at least 5% of the 500 data points displayed
on screen, V
top
defaults to the maximum voltage (V
maximum
) and V
base
defaults to the minimum voltage (V
minimum
) found on the display. An
example of this case would be measurements made on sine or triangle waves.
From this information, the instrument can determine the 10%, 50%, and 90%
points, which are used in most automatic measurements. The V
top
or V
base
of
the waveform is not necessarily the maximum or minimum voltage present on
the waveform. If a pulse has a slight amount of overshoot, it would be wrong
to select the highest peak of the waveform as the top because the waveform
proper rests below the perturbation.
The Scope Auto Measure Menu
Automatic measurement algorithms
7-99