[time-nuts] Re: Counter internal resolution error

[Bob Camp]

Hi

Some of the HP counters have a leakage path between the reference input and 
the measurement inputs. This shows up as frequency measurement issues at
the reference frequency and at other frequencies with fractional relations to it.

Bob

> On Mar 17, 2023, at 7:03 PM, Demetrios Matsakis via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>   On fact one of our best engineers concluded that there was leakage
>   across the inputs, as Magnus mentioned.  I thought at the time he had
>   measured it, but I am not 100% sure of that.
> 
>     On Mar 17, 2023, at 13:47, Magnus Danielson <magnus at rubidium.se>
>     wrote:
> 
>   
> 
>     I also recall one paper relating to laser ranging measurement of the
>     moon which also looked at temperature dependence of counters, and
>     SR620 showed more sensitivity than some other counters. For some
>     measurement purposes, the impact is less than for others.
> 
>     A fun experiment would be to use a delay-stepper to plot this. I
>     accumulated equipment for that over the years, with increasing
>     resolution and performance but never got around to it. Good little
>     practical experiment now that I was able to steer the Colby DL10
>     programmable trombone delay.
> 
>     There is two common reasons for non-linearity, one is from the
>     interpolator itself where error-pulse shaper as well as
>     pulse-to-voltage converter has non-linearities. Another one is du to
>     leakage of either clock or other input shifts the trigger point due
>     to lacking isolation. Such non-linearities can be handled through
>     measurement setup and at times with averaging.
> 
>     Some properties can be managed through wise use of the
>     autocalibration.
> 
>     Then again, most of the times I do not bother to go the extra
>     stretch, but it is good to know the effects are there so one can
>     consider them and if needed cope with them.
> 
>     So, time to close down computer, check out and leave Vancouver after
>     a WSTS conference.
> 
>     Cheers,
>     Magnus
> 
>   On 2023-03-17 16:57, Demetrios Matsakis wrote:
> 
>     I don’t know how SR counters are today, but when we were upgrading
>     our infrastructure over a decade ago we found other counters had
>     better linearity.  Rover et al’s open source article has a good
>     discussion of these issues, although of course you need to have one
>     if you are going to experiment.  See   G. D. Rovera, M. Siccardi, S.
>     Romisch, and M. Abgrali, “Time delay measurements: estimation of the
>     error budget”, Metrologia 56, 2019 035004
> 
>   On Mar 17, 2023, at 9:46 AM, Magnus Danielson via time-nuts
>   [1]<time-nuts at lists.febo.com> wrote:
> 
>   Dear Michael,
>   On 2023-03-16 08:17, Michael Wouters via time-nuts wrote:
> 
>     Dear time-nuts
>     Counter specs often include an “internal resolution” error. For
>     example,
>     the SR620 specs say that it is 25 ps in single-shot, but this can be
>     reduced to 4 ps with sufficient, repeated measurements. Can anyone
>       offer
>     any enlightenment as to the origin of this error, and the
>     statistical
>     distribution it has? I mentioned the SR620 but information about the
>     53230A
>     would be interesting too.
> 
>   First of all, the single-shot resolution is somewhat of a hallmark
>   measure when it comes to counters.
>   The interpolator resolution is part of this, but consider that there
>   exists non-linearities in the interpolator which makes the error
>   larger. I recall there being a plot of the non-linearity in the SR620
>   manual.
>   It is not uncommon to have interpolator resolution better than
>   non-linearities, but the later may be more subtle to most.
>   Averaging can help, but depending to specifics, it's hard to give a
>   number.
>   Cheers,
>   Magnus
> 
>     Cheers
>     Michael
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