[time-nuts] Traceable to NIST...??
wb6bnq at cox.net
Mon Jun 28 22:46:44 UTC 2010
The concept of "traceable to NIST" merely means you have a reference PATH back to
NIST. The level of accuracy to which you claim would still need to be
characterized and specified should you publish any claims as to having calibrated
some piece of equipment.
The purpose of claiming traceability is to state that you have followed
standardized procedures of verifying your in-house references to that of some
recognized higher authority. In the United States that recognized authority is
It is important to note that NIST does not "calibrate" anything in the classical
sense like you would expect a local calibration facility to do. What they
provide is a comparison to their standards. That is to say they will, assuming
you have enough money, make a comparison of your "so-called" standard to their
standard and produce a report stating a current value with an error estimate and
the conditions under which such report is valid (i.e., temp, humidity, etc.).
Clearly, they are only going to accept items that meet certain qualifications.
While they do perform such services, mostly their work is in the research and
theoretical categories as an effort to improve their standards and find ways to
do such in as economical way as possible and still meet or exceed their current
levels of accuracy, resolution and repeatability.
One clear example is the replacement of standard voltage cells with the Josephson
junction process which is easily reproducible and very repeatable. The old cells
required a lot of man hours to maintain and constantly measure to achieve a mean
value out of a number of such cells held at a constant temperature in an oil
bath. It was a lot of number crunching to achieve 1ppm and very few labs were
able to truly maintain a repeatable value below 1ppm.
Another, more relevant to timenuts, is the constant improvement of frequency
Michael Baker wrote:
> Hello, Time Nutters--
> Traceable to NIST...? All you need is this LPRO Rb osc being
> disciplined by a GPSDO and you can claim NIST traceability?
> Not the way I understand the rules....
> What say the list?
> Mike Baker
> > Todayâs communication devices and protocols often require
> > an accurate timebase. Leveraging the best technology of
> > yesterday and today, we are proud to bring you the world's
> > first rubidium GPSDO under $500! The LPRO-101 by EfratomÂ®
> > /SymmetricomÂ®, stabilized by a high-sensitivity GPS system,
> > provides affordable, traceable precision. Watch our DEMO
> * Features: Guaranteed Accurate to < 5x10-11,
> Traceable to NIST when LED is green
> * Typical accuracy is even better â Typical Accuracy Charted
> * Low phase noise 10 MHz, 50â¦ BNC output at +7 dBm
> * Includes power supply and high-gain GPS antenna
> * Phase Locked for absolute accuracy over long time intervals
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