Tektronix, Inc. P6240, Руководство пользователя

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TLS 216 User Manual
B–1
Appendix B: Algorithms
The TLS 216 Logic Scope can take 28 automatic measurements. By knowing
how the instrument makes these calculations, you may better understand how to
use your instrument and how to interpret your results.
Measurement Variables
The logic scope uses a variety of variables in its calculations. These include:
is the value used as the 100% level in measurements such as fall time and
rise time. For example, if you request the 10% to 90% rise time, then the logic
scope will calculate 10% and 90% as percentages with
representing 100%.
is the value used as the 0% level in measurements such as fall time and rise
time.
The exact meaning of and depends on which of two calculation
methods you choose from the Measure menu’s High-Low Setup item. These are
Min-max and Histogram.
Min-Max Method defines the 0% and the 100% waveform levels as the lowest
amplitude (most negative) and the highest amplitude (most positive) samples.
The min-max method is useful for measuring frequency, width, and period for
many types of signals. Min-max is sensitive to waveform ringing and spikes,
however, and does not always measure accurately rise time, fall time, overshoot,
and undershoot.
The min-max method calculates the High and Low values as follows:
= and =
Histogram Method attempts to find the highest density of points above and below
the waveform midpoint. It attempts to ignore ringing and spikes when determin-
ing the 0% and 100% levels. This method works well when measuring square
waves and pulse waveforms.
The logic scope calculates the histogram-based and values as follows:
1. It makes a histogram of the record with one bin for each digitizing level (256
total).
2. It splits the histogram into two sections at the halfway point between
and (also called ).
High, Low