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J P C L / A p r i l 2 0 0 5 / P C E 27www.paintsquare.com
andheld coating thickness gages are common
inspection tools used by applicators and
inspectors. With a little care and mainte-
nance, mechanical and electronic gages can be relied upon to
give many years of dependable service.
This article focuses on maintaining
electronic gages.
Don’t Wait To CalibratePrior to first use, and occasionally
thereafter, it is always a good idea to
review the instruction manual to famil-
iarize yourself with an instrument’s
features and capabilities. Record the
make, model, serial number, and date of
purchase inside the manual, and high-
light maintenance and calibration tips.
Now is the best time to establish a calibration interval.
Calibration is the act of measuring known coating thickness
standards (called “calibration” standards) and verifying that
the results are within tolerance. How often the gage should
have its calibration checked depends upon many factors,
including frequency of use; the application in question; and
the level of care taken during use, handling, and storage.
If you use your coating thickness gage frequently, measure
coatings on abrasive
s u r faces, or use the
gage roughly, your
gage may require a rel-
atively shorter calibra-
tion interval. Make
your calibration inter-
val longer if your gage
spends most of its time
on the shelf. If you are
uncertain about how
often to calibrate the
gage, start with a one-
year calibration inter-
val from the date of
calibration, date of
purchase, or date of
receipt.
What do you do at
these intervals? That
depends upon the quality system you have in place. Some
owners simply measure a sample part when the gage is new
and record the result. This sample is then saved and used to
regularly check the operation and accuracy of the gage.
The best and most universally accepted method, however,
is to measure calibration standards according to a docu-
mented procedure. Calibration standards are available as
either certified coated metal plates or plastic shims. Coated
metal plates are usually more accurate. The process of mea-
suring them is described in a document called a “Calibration
Procedure,” which some manufacturers give upon request at
no charge. Alternatively, you can return the instrument to
the manufacturer or to a qualified lab to have this work per-
formed for a nominal fee.
Use ItÑDon’t Abuse ItNow that you have taken care of the paperwork, take prac-
tice measurements with the test panels or shims that came
with your coating thickness gage. You can even use office
furniture or other handy coated parts to ensure the gage
works properly and that you are using it correctly.
Gages come in all different shapes and sizes. So get to know
the proper way to hold and operate your particular model. The
majority of hand held instruments take one measurement at a
time. Lift the probe away from the surface between measure-
ments. Dragging the probe reduces probe life.
Once the gage has been put into service, it should always be
inspected prior to use. Look for obvious damage, particularly to
the probe or probe cable. Constant-pressure probes should
move up and down freely. While the gage body can work even
when scratched, nicked, or covered with paint overspray, the
probe cannot. So examine the probe carefully. Pay particular
Looking After Your Coating Thickness Gage
Equipment Ma i n t e n a n c e
HBy David Beamish, DeFelsko Corporation
Continued
An electronic, handheld coating thickness gage
Calibration standards are available as either coated metal plates (top)
or plastic shims (bottom)Photos courtesy of the author
Wrong Way Correct Way
For best results and longest life, grip the sliding probe sleevewith your fingers low to the surface.
J P C L / A p r i l 2 0 0 5 / P C E28
Equipment Maintenance
attention to the surface that comes into
contact with the coating. Damaged,
scratched, or worn probes should be test-
ed for accuracy and replaced when neces-
s a r y. Metal filings, dust, and paint should
be carefully removed with a cloth.
Hot and rough surfaces are most
harmful to coating thickness probes.
For longest life, avoid prolonged expo-
sure to hot surfaces and allow the probe
to cool between measurements. Respect
rough surfaces by lowering the probe
carefully and by never dragging it side-
ways. Plastic shims of known thickness
can be placed onto these surfaces to
afford the probe some protection. The
gage will measure the total shim and
coating thickness, but the thickness of
David Beamish is general manager ofDeFelsko Corporation,a New York-based man-ufacturer of handheldcoating test instrumentssold worldwide. He hasa degree in civil engi-
neering and more than 17 years of experi-ence in the design, manufacture, and mar-keting of coating test instruments for a vari-ety of industries, including industrial paint-ing, quality inspection, and manufacturing.He conducts training seminars and is anactive member of various organizations,including SSPC, NACE, ASTM, and ISO.
the shim can be subtracted from the
measured thickness. Be mindful of the
additional measurement tolerance
resulting from use of the shim.
Indications that a gage may need ser-
vice include lower than expected read-
ings (often a sign of probe wear), higher
than expected readings (foreign materi-
al may be stuck on the probe), and
erratic measurements (a possible sign of
a component failure).
Before You Store ItIt is a good idea to take one final look at
the probe before putting the instrument
away. Fresh paint or other adherent
materials can be removed, and prob-
lems can be dealt with immediately,
thus preventing a nasty surprise the
next time you go to use the gage.
It is usually okay to leave batteries
installed and probes attached during
short periods of non-use. Return the
gage to its pouch or to the original pack-
aging. Cover the probe. Store the instru-
ment in a dry location away from mag-
netic fields and extremes of tempera-
ture. When retrieving it for the next
job, make a quick operation check on a
known thickness. This precludes the
need for periodic scheduled mainte-
nance. And don’t forget to bring along
the manual and extra batteries.
Whether magnetic, eddy-current, or
ultrasonic, a coating thickness gage
requires only a modest amount of regu-
lar attention to ensure years of accu-
rate and reliable service.