CHAPTER
7 Analyzing Harmonic Distortion
A
C waveform analysis on an oscilloscope may sound like a pretty sophisticated
procedure. And indeed it is, but not for the user, because the sophistication
occurs within the instrument itself. It’s therefore a practical troubleshooting pro-
cedure for any marine electrician or a boatowner committed to running an electrically
efficient boat.
When you think of oscilloscopes (commonly called scopes), you may picture the bread-
box-size instruments of long ago. But as with all things electronic, the scopes used today
have come a long way. Vacuum tubes are ancient history, and transistors and computer
chips have taken over, enabling vendors to make some small, yet excellent, handheld devices
that really perform. These units are not in the low-priced gear category, although I’ve seen
some advertised for as little as $300. The unit that’s shown in this chapter is from the Fluke
860 series, and costs about $2,000. (Note: This has recently been replaced by the 190 series.)Do You Need a Scope?
On a modern boat, AC can be supplied by a variety of sources, and sometimes even a com-
bination of sources. Shore power is only one part of the picture. AC generators, DC-to-
AC inverters, and converters that modify incoming voltage and frequency are becoming
mainstream—even on boats that historically were considered too small to bother with
dockside power.
Unless you do a lot of work on complex AC systems with inverters, generators, and
transformers that perform voltage and frequency conversions, an oscilloscope should
not be the first tool on your wish list. You can get almost as much utility from a high-
end multimeter with a “peak hold” feature and data-logging capability. For those who
would like to get into the oscilloscope game without investing several thousand dollars,
I recommend the Extech 381 series scopes, which cost approximately $250 to $400.190 series, Fluke, http://www.fluke.com (replaces the 860 series)
381 series, Extech Instruments, http://www.extech.comOSCILLOSCOPESCopyright © 2007 by Edwin R. Sherman. Click here for terms of use.