Tektronix TDS 684A, TDS 744A, TDS 784A HighRef, MidRef, LowRef, Mid2Ref

Appendix B: Algorithms
B–2 TDS 684A, TDS 744A, & TDS 784A User Manual
The oscilloscope 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 ).
3. The level with the most points in the upper histogram is the  value, and
the level with the most points in the lower histogram is the  value.
(Choose the levels where the histograms peak for  and )
If  gives the largest peak value within the upper or lower histogram, then
return the  value for both  and  (this is probably a very low
amplitude waveform).
If more than one histogram level (bin) has the maximum value, choose the
bin farthest from .
This algorithm does not work well for two-level waveforms with greater than
about 100% overshoot.
The user sets 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% or 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.
HighRef, MidRef, LowRef,
Mid2Ref