Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 189)

Wave Expert
WE-OM-E Rev A
187
Averaging Waveforms
Summed vs. Continuous Averaging
For Summed averaging, you specify the number of acquisitions to be averaged. The averaged data
is updated at regular intervals and presented on the screen.
On the other hand, Continuous averaging (the system default) helps to eliminate the effects of
noise by continuously acquiring new data and adding the new waveforms into the averaging buffer.
You determine the importance of new data vs. old data by assigning a weighting factor. Continuous
averaging allows you to make adjustments to a system under test and to see the results
immediately.
Note: Continuous Averaging is accessible from the channel "Vertical Adjust" dialog under "Pre-Processing," and from the
math function menu.
Summed Averaging
Summed Averaging is the repeated addition, with equal weight, of successive source waveform
records. If a stable trigger is available, the resulting average has a random noise component lower
than that of a single-shot record. Whenever the maximum number of sweeps is reached, the
averaging process stops.
An even larger number of records can be accumulated simply by changing the number in the dialog.
However, the other parameters must be left unchanged or a new averaging calculation will be
started. You can pause the averaging by changing the trigger mode from NORM/AUTO to STOP.
The instrument resumes averaging when you change the trigger mode back to NORM/AUTO.
You can reset the accumulated average by pushing the CLEAR SWEEPS button or by changing an
acquisition parameter such as input gain, offset, coupling, trigger condition, timebase, or bandwidth
limit. The number of current averaged waveforms of the function, or its zoom, is shown in the
acquisition status dialog. When summed averaging is performed, the display is updated at a
reduced rate to increase the averaging speed (points and events per second).
Continuous Averaging
Continuous Averaging, the default setting, is the repeated addition, with unequal weight, of
successive source waveforms. It is particularly useful for reducing noise on signals that drift very
slowly in time or amplitude. The most recently acquired waveform has more weight than all the
previously acquired ones: the continuous average is dominated by the statistical fluctuations of the
most recently acquired waveform. The weight of ‘old’ waveforms in the continuous average
gradually tends to zero (following an exponential rule) at a rate that decreases as the weight
increases.
The formula for continuous averaging is
new average = (new data + weight * old average)/(weight + 1)
This is also the formula used to compute summed averaging. But by setting a "sweeps" value, you
establish a fixed weight that is assigned to the old average once the number of "sweeps" is reached.
For example, for a sweeps (weight) value of 4: