21 5.5 Minute Histograms
line or load profiling. For these histograms, the few cycles at the extremes are
usually unimportant: the vast majority in the middle is the good data.
5.5 Minute Histograms
The Minute Histogram provides a much “smoother” version of the Cycle His-
togram. Quick sags and swells are averaged out of the data, to show the
nominal voltage or current level every minute. Voltage regulation problems
are easy to see in the Minute Histogram.
5.5.1 What’s Recorded
The Minute Histogram is similar to the Cycle Histogram. During each minute
of the recording session, the voltage is averaged (every cycle is included).
At the end of the minute, the Histogram bin counter for that average value
is incremented. The result is a Histogram of one minute average voltages,
instead of one cycle voltages. For example, if the voltage were 123 volts for 55
seconds, then 115 volts for 5 seconds, the average would be 122 volts, and the
122 volt bin counter would be incremented. If the Stripchart interval is also
set to one minute, then the Stripchart voltage averages will match the Minute
Histogram counts.
Like the Cycle Histograms, there are no settings for the Minute Histogram.
All available Minute Histograms in a Scanner are always recorded, regardless
of the settings for any other record types. Memory does not run out for a
Minute Histogram; it just keeps classifying measurements into the bins (by
incrementing the bin counters) as long as the recording session lasts.
All Scanners record a voltage Minute Histogram. Scanners that can mea-
sure current also record a current Minute Histogram.
5.5.2 Suggested Uses
The voltage Minute Histogram can reveal voltage regulation problems. Ide-
ally, the line voltage should be at the same value every minute. The larger the
spread in the Minute Histogram, the more the voltage is varying. The center
of the spread is (hopefully) the target regulation voltage. This information is
also present to an extent in the voltage Stripchart, depending on the record-
ing interval and amount of memory. Because the Stripchart spreads out the
voltage averages as a time graph, it can be more difficult to gauge how long
the voltage was at certain levels (although it may be easier to see why the
voltage was moving).
