[time-nuts] HP53132A vs SR625

[Volker Esper]

Hi,

I just powered on my SR and looked for the offset, when the 10 MHz 
reference is connected to the input (at a gate time of 1s without 
further averaging). It shows an offset of 0 to 400uHz which should 
represent a mean error of 2E-11, while the manual predicts an error of 
about 1E-10 (as Said told us, and as my manual tells me). That's within 
the spec.

Unfortunately I don't have a 53132, but the manual of the HP predicts an 
error of E-10 - just the same value as with the SR.

If I was a manufacturer of such a counter, I wouldn't show the digits 
beneath the predicted error, but SR does: it shows 13 digits. How many 
digits does the HP show? Could it be, that the HP shows one or two 
digits less at this measurement? With only 11 digits displayed, the SR 
wouldn't show any offset, too.

By the way, HP's 100ps isn't the worst case value - that is 500ps.

So, what's the big difference beetween them?
- the predicted error is the same for both (or am I wrong?).
- my SR is within it's specification at 10 MHz (I did the calibration 
myself).
- the uncertain digits (below 1mHz, in this case) are within the error 
spec, and I guess they are uncertain because they come from an analog 
circuitry (namely the interpolation circuitry). The statement, that a 
counter only has to count zero crossings and nothing else, isn't right 
at that point, and that's the case for both,
- and they both have to deal with the analog stuff, such as noise and so on

Again, since I don't have a 53132 I can't compare the counters directly, 
I was just a little concerned about a discussion - no offense! - that 
compares apples and oranges.

Thank you for a still inspiring discussion!

Volker





Am 17.03.2013 20:05, schrieb SAIDJACK at aol.com:
> Ed,
>
> the calculation is the same, however the numbers are 100ps for 53132A
> versus 350ps, and I have not seen an average systemic offset being displayed on
> any of the 3x 53132A units I use, and I see one on the SR-620. That's  why
> I sent it into SRS for calibration, paid the $$$ and got it back with the
> same exact offset and a statement that it is operating within specifications
> so  no adjustment is necessary.
>
> HP manages to show zero error on average, with the digits bouncing back and
>   forth. The SRS unit manages to show a hard frequency offset. If I remember
>   correctly the SR-620 even shows this offset with it's own reference
> connected to  the inputs, the HP does not.
>
> bye,
> Said
>
>
> In a message dated 3/17/2013 11:26:16 Pacific Daylight Time,
> ed_palmer at sasktel.net writes:
>
> Hi  Said,
>
> That equation looks similar in form to the specs for any counter.  What
> are the comparable equations for the  53132A or the 5370(A or  B)?
>
> Ed
>
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