Stage Micrometers and Glass Scales
Be sure to use appropriate calibration aids and standards
SPI Supplies is pleased to offer the product lines of the world's leading manufacturers of both calibrated
glass scales (PEAK) and stage micrometers (Graticules, Ltd, now known as Pyser-SGI). In both cases, if you
make a purchase, you can be sure that you truly are purchasing the highest quality measuring instrument money
can buy. And it would be at reasonable prices.
Certified vs. Traceable products
Note that wherever possible, these fine products for calibration are
available not only as "traceable" standards but also as "certified"
standards. There is a significant increase in cost for "certified" over
"traceable" products. First, in general, except perhaps for the package it
comes in, the purchaser is getting the same thing. When the tool is sold as
being "traceable", it means that the manufacturer made verifying
measurements with their own microscopes that had themselves been calibrated
with standards traceable back to a national standards body such as NIST, NPL, NRC, etc.
But if the product is offered "certified", this means that particular item
was given to an agency accredited to do such certifications, at which a series of individual
measurements are made on that particular item of product, with standard
deviations reported and other details of the measurements described on a
"Certificate of Calibration". This certificate stays with the product from
that time on, since it describes the details of that particular item of
calibration.
For the stage micrometers, for example, which are available "certified",
they can be purchased certified either by the NPL (National Physics
Laboratory) in the UK or by an independent laboratory accredited by
UKAS (United Kingdom Accreditation Service) to conduct these kinds of certifications. Is one certification "better"
than the other? Most would consider a certification by NPL to be a "higher level"
certification than one by the UKAS - accredited laboratory. On the other hand, we are unaware of
any instance where a certification by the UKAS - accredited laboratory was not accepted by an inspector
accrediting a laboratory. Most of our customers seem to be happy with the
certification coming from the independent laboratory but on occasion, one does demand the NPL (and
more expensive) certification.
We therefore leave the decision as to which level of certification they
should be purchasing strictly up to them. If you have a laboratory that is
dedicated primarily for teaching purposes, or a laboratory for which there
is no chance of its ever being accredited under one of the ISO directives,
quite possibly the "traceable" product is going to be just fine.
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Tuesday February 09, 2010
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