Dso Process; Parameter Buffer - LeCroy SDA Operator's Manual

DSO Process

This instrument can be used to generate histograms of the parameter values of input waveforms.
The follwing items must be defined before doing so:
•
The parameter to be histogrammed
•
The trace on which the histogram is to be displayed
•
The maximum number of parameter measurement values to be used in creating the
histogram
•
The measurement range of the histogram
•
The number of bins to be used
Some of these items are pre-defined, but can be changed. Once defined, the oscilloscope is
ready to make the histogram. The sequence for acquiring histogram data is as follows:
1. Trigger
2. Waveform acquisition
3. Parameter calculations
4. Histogram update
5. Trigger re-arm
If you set the timebase for non-segmented mode, a single acquisition occurs prior to parameter
calculations. However, in Sequence mode an acquisition for each segment occurs prior to
parameter calculations. If the source of histogram data is a memory, saving new data to memory
effectively acts as a trigger and acquisition. This only takes place one time per second because
updating the screen can take lots of processing. This also minimizes trigger dead time. Under
remote control operation, the display can be turned off to maximize measurement speed.

Parameter Buffer

The oscilloscope maintains a circular parameter buffer of the last 20,000 measurements made,
including values falling outside the set histogram range. If the maximum number of events to be
used for the histogram is a number `N' less than 20,000, the histogram is continuously updated
with the last `N' events as new acquisitions occur. If the maximum number is greater than 20,000,
the histogram updates until the number of events is equal to `N.' Then, if the number of bins or
the histogram range is modified, the scope uses the parameter buffer values to redraw the
histogram with either the last `N' or 20,000 values acquired (whichever is the lesser value). This
allows the parameter buffer to redisplay histograms using an acquired set of values and settings.
This produces a distribution shape with the most useful information.
In cases where the optimal range is not apparent, the scope has a powerful range finding
function. If required, the values in the parameter buffer are examined to calculate an optimal
range and redisplay the histogram. The instrument also provides a running count of the
parameter value amounts falling within, below, or above the range. Values falling below or above
the range can then be recalculated by the range finder to include these parameter values (as long
as they are still within the buffer).
SDA-OM-E Rev H
SDA Operator's Manual
133