Additional Advantages
While our primary focus is identifying inter-
mittent problems, having a PC or laptop link-
up has other advantages. For example, the
larger screen of a computer versus a meter
magnifies your view dramatically. This is par-
ticularly useful when looking for distortion in
AC waveforms. Even if your multimeter oscil-
loscope has the technical capability to capture
subtle problems, the size of the display (2 to
4 inches, typically) may make it difficult to
observe. But if you blow up the view on a 14-
or 15-inch PC or laptop screen, those prob-
lems become obvious. For example, the flat-
tening at the peak of the wave shown in the
top photo on page 81 is easy to see when mag-
nified on a computer screen but would be hard
to see on a 2- to 4-inch multimeter display.
If you are a professional technician, sending
data logs to a computer opens up several possi-
bilities. You can save and print customer files,
include screen shots in a customer’s report, or
improve your internal documentation and
quality control processes. It’s easy to do, and it
adds a level of professionalism to your work
that is unprecedented in the marine field.
Real-World Examples
Let’s look at some real-world cases where you
might consider data logging as a useful aid in
troubleshooting.
Example 1: Unexplained Underwater
Metal Corrosion
One of the classic problems affecting boats in
marinas is rapid, unexplainable corrosion of
underwater metal components. Often, when
going through a complete corrosion analysis,
you may find no measurable problem. The
problem could be cycling of appliances or
equipment, such as an air conditioner or bilge
pump, either on your own boat or one nearby
at the dock. So what do you do?
You want to capture stray current in the
water surrounding the affected boat “after
hours.” Link a tracking multimeter, fitted with
a special silver/silver chloride reference elec-
trode (see Chapter 11), to your computer, and
immerse the electrode in the water near the
affected boat. The computer link-up will
record the data, allowing you to either confirm
or rule out the presence of stray current. If
there is stray current, you’ll be able to pinpoint
the exact time and date of the measurement.
More important, you will have confirmed a
probable cause of corrosion, without having to
make five repeat trips to the boat to try and
“catch” the problem. And, if you’re a techni-
cian, you avoid having to report to the client
that “no problem was found at the time of sur-
vey.” Or if you’re a do-it-yourselfer, you won’t
have to hang out on the boat all night, looking
at the multimeter readout every 10 minutes.
Example 2: Instrument Lighting That
Fails Only When Underway
In this example, the backlighting on your dash-
mounted engine monitoring instruments
blinks on and off when motoring in rough sea
conditions. Most people would immediately
attribute this problem to a loose electrical con-
nection feeding the lights. But a look at the
electrical feeds to the dash lights has come up
with nothing, and the size and complexity of
the boat’s overall wiring make it difficult to
inspect every connection for every wire. Fur-
ther complicating the diagnosis is the fact that
the instruments are backlit by LEDs mounted
on a printed circuit board. The problem might,
therefore, be in the power supply or ground
return for the PC board, or it might be on the
board itself, which is sealed and integrated with
the backside of the instrument housing.
To troubleshoot this problem, you should
log data while reproducing the conditions in
which the problem occurs. Attach a data-logging
multimeter to the power supply and ground it tousing a laptop 85