[time-nuts] R&S XSRM Rubidium Standard

KA2WEU at aol.com KA2WEU at aol.com
Sun Sep 17 14:44:44 EDT 2017

good point 
In a message dated 9/17/2017 2:01:01 P.M. Eastern Daylight Time,  
jimlux at earthlink.net writes:

On  9/17/17 9:42 AM, KA2WEU--- via time-nuts wrote:
> Simply call it " Make  it to meet specification", N1UL
> In a message dated 9/17/2017 12:39:32 P.M. Eastern Daylight  Time,
> magnus at rubidium.dyndns.org writes:
> Hi,
> The word "calibration" is overloaded with multiple  meanings,  and
> incompatible too.
> "calibration"  can thus imply different things.
> I  regularly see people  use these terms inconsistently. That people get
> disappointed when they  get the wrong thing is to be  expected.
> Cheers,
>  Magnus

Indeed - in my business, we have to be careful  about the word "test" vs, 
say, "characterization".  A "test" has a  pass/fail criteria associated 
with it, while a "characterization" might  just need recording what the 
value is.  "tests" have institutional  requirements for witnessing, etc. 
that "characterizations" do not, for  instance.

And this gets into the whole "knowledge" vs "control" - I may  not care 
if a XO changes frequency 10ppm over temperature, as long as it's  
repeatable and I can know the actual frequency within 0.5  ppm.

As Magnus points out, "calibration" can mean many different  things, and 
some of them are historically derived.  Back in the day,  there may have 
been some sort of physical adjustment required to, for  instance, set the 
scale factor of a display - but now, it's "calibrated by  design", and 
the "calibration process" (as in "sending it to the cal lab"  to get a 
"cal cert") is more about verification that it's not  "broken".

I also used to (and still do) get bent out of shape when  you'd send 
something like a power supply out for cal, and it would come  back with 
some problem (like a non-functioning pilot light).  And the  cal lab 
would say: "we checked the output voltage and it is within  spec".  Yeah, 
but isn't "proper function of all features" covered -  and the response 
would be "no, it is not, we don't see 'verify function of  pilot light' 
on the cal procedure we have"

ANd then there's the  "calibration/validation" phase of instruments in 
space - that's a  completely different kind of thing, more akin to 
characterization.. The  'val' part is yes, verifying that the instrument 
is working as  designed,but the 'cal' part is more about relating 
instrument measurements  to some other reference, and from that, relating 
it to some physical  property of interest.  And that can happen at many 

A  spaceborne scatterometer to measure winds can be cal/val at
1) Does the  instrument work, and are the instrumental effects accounted 
for - if it  measure a particular backscatter cross section, is that what 
the  backscatter cross section really is?
2) Does the "retrieval model function"  that turns backscatter 
measurements into wind speed and direction  work?

And particularly for #2, a lot of it is inferential - comparing  one 
model against another, since there's not really "ground truth"  available.

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