The PXIe-5840 Specification for its Internal Frequency Reference specifies accuracy in a table of unitless numbers. Is this meant to be interpreted as fractional uncertainty, or something else?
Most NI guides I have found on frequency accuracy suggest it will be specified as PPM but that does not seem to be the case here.
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1e-6 is an alternate notation for 1ppm.
Source and more info: https://www.rapidtables.com/math/number/PPM.html
Spex, Thanks for the quick response. Sure, I agree that’s the obvious interpretation absent of anything in the spec saying that is how the data should be interpreted, but I was hoping to get confirmation this is in fact what NI intended.
You can consider it confirmed the intention was to represent the frequency stability spec as a fractional uncertainty (ppm). I'm not sure why some NI manuals use the ppm nomenclature and others use N * 10^-6. The initial adjustment accuracy is relative to the frequency of interest, e.g. for a frequency of 1GHz, the uncertainty is +/- 200ppb * 1GHz or 200 Hz.
So I can better understand your concern and provide feedback to the spec process, how else would you consider interpreting that spec?
Spex, Thanks for the detailed response. This certainly clears things up. Sorry, I missed the that you were responding for NI in the first reply.
I guess it would be good if they were consistent across all product specifications in how that type of information is presented. Thanks again for your reply!
Glad I could clear things up. I agree with your feedback about consistency. I'm not sure if different domains prefer to publish that type of spec slightly differently, or why we have inconsistencies. I tried to do some background work, and I did see that that there is some debate in the engineering community about ppm and ppb as acronyms because they are not part of any formal SI unit standardization. The m and b are not consistent with "nano" nor "pico" nor "Giga" nor "Mega" prefixes that are standardized in SI, and million and billion are language specific. So in that sense, the N * 10^-6 notation is more universal, even if it is less well known.