The exact value of Base and Top depends on which Base Top Method you select in the Reference Levels panel of a Measurement
configuration menu. It also depends on if you set the reference level to be Global (applies to all measurements set as Global in the
Reference Levels panel), or Local (just applies to the measurement that is set to Local).
Base, Top calculation methods
The Base Top calculation method is set in the Reference Levels panel of a Measurement configuration menu.
Auto is the default method, and automatically determines the best Base Top method to use. Most commonly sets the Base Top method to
Histogram Mode.
MinMax defines the 0% and the 100% waveform levels as the lowest value and the highest value samples of the waveform record. This
setting is best for examining waveforms that have no large, flat portions at a common value, such as sine waves and triangle waves -
almost any waveform except for pulses.
The MinMax method calculates the Top and Base values as follows:
Top = Max
and
Base = Min
Histogram uses histogram analysis to select the most common values either above or below the midpoint. Since this statistical approach
ignores short-term aberrations (overshoot, ringing, and so on), Histogram is the best setting for examining pulses.
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.
Edge calculations
Edge1, Edge2, and Edge3 refer to the first, second, and third Mid reference edge times, respectively.
Measurement concepts
3 Series Mixed Domain Oscilloscope Printable Help
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