20 5 WHAT THE 2SX-SERIES SCANNER RECORDS
count of at least six in the Histogram at 108 volts. The count will probably
be somewhat larger, unless each sag was only one cycle long.
There are no settings for Histograms. All available Histograms in a Scan-
ner are always enabled, regardless of the settings for any other record types.
Memory does not run out for a Histogram; it just keeps classifying measure-
ments into the bins (by incrementing the bin counters) as long as the recording
session lasts.
The neutral to ground voltage channel on the 2SX-Series Scanner records a
histogram with tenth-volt increments, from 0.0 to 90.0 volts.
5.4.2 Suggested Uses
The power of the Histogram is that every cycle is included in the report. Every
cycle during the recording session is reflected in the count of one of the bins.
If all the counts in a Histogram are totaled, the result is how many cycles the
recording session lasted (minus any time under a power outage).
Histograms are presented as a bar graph and a report. The report is in
some ways easier to read than the graph. The absolute highest and lowest
voltages during the recording session are found by finding the highest and
lowest bins with a non-zero count. At that point you also know how many
cycles the voltage was at those extremes, and by glancing at the nearby bins,
you know how many cycles the voltage was near those extremes. For example,
if all the bins below 110 volts are zero, then you immediately know that there
was not even a single cycle of voltage below 110 volts anytime during the
recording session. If the count at 111 volts is 1,352,200, then the voltage was
at 111 volts for over 6 hours (1; 352; 200=(60 ‡ 60 ‡ 60)). By totaling the
counts for all the bins in a voltage range (for example, 0 to 90 volts), you find
how many cycles the voltage was in that range.
More complicated power quality questions can be answered by exporting
the histogram data to a spreadsheet. By dividing each count by the total of
all the counts, the histogram data is normalized, and can represent a sample
probability distribution function. If a normal, or bell-shaped probability dis-
tribution is fit to this data, a standard deviation is created that can be used
to answer “what high and low limits does the line voltage meet 99.99% of the
time?”. A cumulative sum over the data will convert the distribution function
into a sample cumulative probability function. Correlations between channels
can be performed by comparing the probability functions of channels.
For the voltage histogram, most of the time the user is interested in the
few cycles that are outside certain limits, not the vast majority of cycles that
are perfectly normal. These few cycles usually represent power quality issues.
The current, power, and power factor histograms are useful for distribution
