Certification of Stage Micrometers Offered by SPI Supplies
Selecting the certification agency
For those not familiar with the terminology, there is a big difference in meaning between having a stage micrometer that is described as being "traceable" vs. one that has been "certified."
If it is "traceable", then all of the measurements validating the dimensional calibration are done using standards that are "traceable" back to standards that were directly calibrated against national standards held at one of the world's national standards making bodies such as NIST in the USA , National Research Council in Canada or the National Physical Laboratory in the UK.
For a particular stage micrometer to be "certified", some number of individual measurements are made at a laboratory that has been accredited to do such metrology testing. The mean value is reported along with the standard deviation in the individual measurements. We offer the customer the option of having any of the family of stage micrometers offered by SPI Supplies certified at either the National Physical Laboratory in the UK or at UKAS (United Kingdom Accreditation Service) also in the UK. Both agencies are "recognized" in other countries and therefore in that sense, their acceptance is the same.
However, some customers prefer to have a certification by a prestigious top national agency, not one that they (e.g. NPL) has accredited to do such testing, such as UKAS. In this case, the NPL is the top agency in the UK and they have accredited UKAS laboratories to do this same type of metrology testing. The certification costs to SPI are much higher when the testing is done at NPL, presumably because of their much higher overhead and infrastructure costs, therefore the difference in the pricing.
If you are getting a calibrated stage micrometer to comply with some requirement that is part of an accreditation program, we would suggest discussing the required level of certification with your assessor; getting a higher level certification than what is going to be actually required is just throwing money to the wind (in our humble opinion, that is).
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Tuesday February 09, 2010
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