Measure of Quality
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DeFelsko Corporation does not provide expiration dates on
Calibration Certificates issued with our handheld inspection instruments.
Several non time related factors have shown to be more critical in determining
calibration intervals. These factors are primarily the frequency of use,
the application in question, as well as the level of care taken during use,
handling and storage. For example, a customer that uses the gage frequently,
measures on abrasive surfaces, or uses a coating thickness instrument roughly
(i.e. drops the instrument, fails to replace the cover on the probe tip for storage,
or routinely tosses the instrument into a tool box for storage) may require a
relatively shorter calibration interval.
From both theoretical analysis and practical experience,
the impact of temperature and moisture on the instrument is very minimal. In addition,
manufacturing processes are designed to minimize post calibration changes
in instrument performance. Drift in coating thickness instrument measurement is typically
linear and is thus compensated for prior to use by the “zero” function of
the instrument. For this reason the amount of time the instruments remain on the shelf
(both before purchase and between use) has little significance.
With these factors taken into consideration, DeFelsko recommends
that our customers establish the instrument calibration intervals based upon their
own experience and work environment. Based on our product knowledge, data
and customer feedback, a one year calibration interval from either the date
of calibration, date of purchase, or date of receipt is a typical starting
The transfer to a digital design in the latest version of
the PosiTector® series has enabled us to move all of the
measurement electronics and functionality from the gage body to small circuit
boards within the probe. For this reason, the gage body is now a basic power
source and display that has no impact on the instruments function or calibration.
To address this change, it was necessary to identify the
probe as the true instrument calibrated by our Calibration Lab. That is
why the Calibration Certificate now displays the serial number for the probe
and not for the gage. Historically we have had customers fail Quality Audits
because they chose to mix and match gages, resulting in a gage-probe combination
that did not match the Certificate of Calibration.
For most of our customers and dealers this is an additional
selling feature because it not only allows complete interchangeability between
gage-probe combinations, but it also facilitates sending solitary probes
back for calibration or repair, allowing them to continue with their measurement
processes if they have multiple probes.
One final recommendation for companies with only one gage
body and one probe is to use the probe serial number for both as it is by
far the most critical. Then the unit can be treated as one instrument with
full traceability through the serial number engraved on the probe.
DeFelsko Corporation no longer provides expiration dates
on the Calibration Certificates for our Calibration Standards. Customer
dependent factors have shown to be too critical in establishing calibration
intervals. These factors are primarily the thickness of the standard, frequency
of use, and care taken during use, handling and storage of the Calibration
Calibration data for Calibration Standards used in house
by DeFelsko range from significant wear to our thinnest Calibration Standards
that are used frequently (up to a hundred times per day) to no significant
wear to our thicker standards that are used less frequently (a couple of
times a day). Due to this information we track the thickness of our standards
biweekly, replacing thinner standards (e.g. 0.35 mil) every couple of months
and thicker standards (250 mil) every couple of years.
With all these factors taken into consideration, DeFelsko
recommends that our customers establish their own calibration intervals
based upon their own experience with the Calibration Standards. One year
from either date of calibration, date of purchase, or date of receipt of
a Standard is a typical starting calibration interval selected by our customers.
There are no shelf life concerns with the Coating Thickness
Standards. The technical support staff of the manufacturer (PCWI) has identified
negligible effects due to humidity and temperature on the accuracy of the
standards. Further, our quality control program records for PCWI standards
used in house show no impact due to shelf life, even when standards are
stored in an open production environment. The only factor affecting the
life of PCWI standards is visible wear resulting from excessive use or improper
To address the issue of dates shown on PCWI's calibration
certificates, it is our recommendation that all customers purchasing PCWI
standards begin their calibration intervals on the date of receipt.