Teledyne LeCroy WaveExpert 100H Operators Manual - Manual (Page 128)

Operator’s Manual
126
WE-OM-E Rev A
pks Peaks
Definition: The number of peaks in a histogram.
Description: The instrument analyzes histogram data to identify peaks from background
noise and histogram binning artifacts such as small gaps.
Peak identification is a 3-step process:
1. The mean height of the histogram is calculated for all populated bins. A
threshold (T1) is calculated from this mean, where:
T1= mean + 2 sqrt (mean).
2. A second threshold is determined based on all populated bins under T1 in
height, where:
T2 = mean + 2 * sigma,
and where sigma is the standard deviation of all populated bins under T1.
3. Once T2 is defined, the histogram distribution is scanned from left to right.
Any bin that crosses above T2 signifies the existence of a peak. Scanning
continues to the right until one bin or more crosses below T2. However, if the
bins cross below T2 for less than a hundredth of the histogram range, they
are ignored, and scanning continues in search of peaks that cross under T2
for more than a hundredth of the histogram range. Scanning goes on over
the remainder of the range to identify additional peaks. Additional peaks
within a fiftieth of the range of the populated part of a bin from a previous
peak are ignored.
NOTE: If the number of bins is set too high, a histogram may have many small gaps. This
increases sigma and, thereby, T2. In extreme cases, it can prevent determination of a peak, even
if one appears to be present to the eye.
Example: Here the two peaks have been identified. The peak with the highest
population is peak #1.