LeCroy DDA 7 Zi series, Руководство оператора

Страница: 119 / 544

Operator's Manual
WP700Zi-OM-E-RevA
118
However, signal noise and the use of a high number of bins relative to the number of parameter values acquired,
can give a jagged and spiky histogram, making meaningful peaks hard to distinguish. The scope analyzes
histogram data to identify peaks from background noise and histogram definition artifacts such as small gaps,
which are due to very narrow bins.
Binning and Measurement Accuracy
Histogram bins represent a sub-range of waveform parameter values, or events. The events represented by a bin
may have a value anywhere within its sub-range. However, parameter measurements of the histogram itself, such
as average, assume that all events in a bin have a single value. The scope uses the center value of each bin's
sub-range in all its calculations. The greater the number of bins used to subdivide a histogram's range, the less
the potential deviation between actual event values and those values assumed in histogram parameter
calculations.
Nevertheless, using more bins may require that you perform a greater number of waveform parameter
measurements, in order to populate the bins sufficiently for the identification of a characteristic histogram
distribution.
In addition, very fine grained binning will result in gaps between populated bins that may make it difficult to
determine peaks.
The oscilloscope's 5,000-parameter buffer is very effective for determining the optimal number of bins to be used.
An optimal bin number is one where the change in parameter values is insignificant, and the histogram
distribution does not have a jagged appearance. With this buffer, a histogram can be dynamically redisplayed as
the number of bins is modified by the user. In addition, depending on the number of bins selected, the change in
waveform parameter values can be seen.
Full Width at Half Maximum
fwhm Full Width at Half Maximum
Definition:
Determines the width of the largest area peak, measured between bins on either side of the
highest bin in the peak that have a population of half the highest's population. If several peaks
have an area equal to the maximum population, the leftmost peak is used in the computation.
Description:
First, the highest population peak is identified and the height of its highest bin (population)
determined (for a discussion on how peaks are determined see the pks parameter Description:).
Next, the populations of bins to the right and left are found, until a bin on each side is found to
have a population of less than 50% of that of the highest bin's. A line is calculated on each side,
from the center point of the first bin below the 50% population to that of the adjacent bin, towards
the highest bin. The intersection points of these lines with the 50% height value is then
determined. The length of a line connecting the intersection points is the value for fwhm.