05-26-2022 08:50 AM
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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05-26-2022 09:09 AM
1e-6 is an alternate notation for 1ppm.
Source and more info: https://www.rapidtables.com/math/number/PPM.html
05-26-2022 09:26 AM
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.
05-26-2022 01:52 PM
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?
05-27-2022 08:40 AM
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!
05-27-2022 05:27 PM
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.