Oscilloscope Reference Measurement variables
Low = Min
Histogram method. attempts to find the highest density of points above and below the waveform midpoint.
It attempts to ignore ringing and spikes when determining the 0% and 100% levels. This method works
well when measuring square waves and pulse waveforms.
The oscilloscope calculates the histogram-based High and Low values as follows:
1. It makes a histogram of the record with one bin for each digitizing level (256 total).
2. It splits the h istogram into two sections at the halfway point between Min and Max (also called Mid).
3. The level with the most points in the upper histogram is the High value, and the level with the most
points in the lower histogram is the Low value. (Choose the levels where the histograms peak for
High and Low)
If Mid gives the largest peak value within the upper or lower histogram, then return the Mid value for
both High and Low (this is probably a very low amplitude waveform)
.
If more than one histogram level (bin) has the maximum value, choose the bin farthest from Mid.
This algorithm does not work well for two-level waveforms with greater than about 100% overshoot.
HighRef, MidRef, LowRef, Mid2Ref
You set the various reference levels, through the Reference Level selection of the Measure menu. They
include:
HighRef. the waveform high reference level. Used in fall time and rise time calculations. Typically set to
90%. You can set it from 0% to 100% o r to a voltage level.
MidRef. the waveform middle reference level. Typically set to 50%. You can set it from 0% to 100% or to
a voltage level.
LowRef. the waveform low reference level. Used in fall and
rise time calculations. Typically set to 10%.
You can set it from 0% to 100% or to a voltage level.
Mid2Ref. the middle reference level for a second waveform (or the second middle reference of the same
waveform). Used in delay time calculations. Typically set to 50%. You can set it from 0% to 100% or to
a voltage level.
Other variables
The instrument also measures several values itself t hat it uses to help calculate measurements.
Record Length. is the number of data points in the time base. You set it with the Horizontal menu Record
Length item.
Start. is the location of the star t of the measurement zone (X-value). It is 0.0 samples unless you are
making a gated measurement. Whe n you use gated measurements, it is the location of the left vertical
cursor.
DSA/DPO70000D, MSO/DPO/DSA70000C, DPO7000C, and MSO/DPO5000 Series 727
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