1. It makes a histogram of the record with one bin for each digitizing level.
2. It splits the histogram 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 Top value, and the level with the most points in the lower
histogram is the Base value.
If Mid gives the largest peak value within the histogram, the oscilloscope returns the Mid value for both Top and Base (this is
probably a very low amplitude waveform).
If more than one histogram level (bin) has the maximum value, the oscilloscope chooses the bin farthest from Mid.
This algorithm does not work well for two-level waveforms with greater than about 100% overshoot.
Histogram Eye Center uses histogram analysis of the amplitudes in the center of each bit (unit interval) while ignoring the
waveform during bit transitions. The histogram sets the Top at the nominal high level and Base at the nominal low level. This is
similar to the Histogram Mode, except it is less influenced by the shape of the waveform during transitions between bits.
HighRef, MidRef, LowRef
You set the various reference levels, through the Reference Levels tab of the Measure menu. They include:
High is the waveform high reference level (also HighRef). Used in all measurements. Typically set to 90%. You can set it from
0% to 100% or to a voltage level.
Mid is the waveform middle reference level (also MidRef). Mid reference levels are used in all measurements that need to find
edges. Typically set to 50%. You can set it from 0% to 100% or to a voltage level.
Low is the waveform low reference level (also LowRef). Used in all measurements. Typically set to 10%. You can set it from 0%
to 100% or to a voltage level.
High, mid and low reference levels can be set uniquely for each measurement source. Reference levels can also be set
differently for rising edge detection and falling edge detection.
Other variables
The instrument also measures several values itself that 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 start of the measurement zone (X-value). It is 0.0 samples unless you are making a gated
measurement. When you use cursor gated measurements, it is the location of the left vertical cursor.
End is the location of the end of the measurement zone (X-value). It is (RecordLength – 1.0) samples unless you are making a
gated measurement. When you use cursor gated measurements, it is the location of the right vertical cursor.
Hysteresis Is the hysteresis band of the waveform amplitude.
For example, once a crossing has been measured in a negative direction, the waveform data must fall below the hysteresis value
of the amplitude from the Mid reference point before the measurement system is armed and ready for a positive crossing.
Similarly, after a positive Mid reference crossing, waveform data must go above the hysteresis value of the amplitude before a
negative crossing can be measured. Hysteresis is useful when you are measuring noisy signals, because it allows the
oscilloscope to ignore minor fluctuations in the signal.
Measurement concepts
430 MSO54, MSO56, MSO58, MSO58LP, MSO64 Help
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