[time-nuts] HP 5335A Question
Bob kb8tq
kb8tq at n1k.org
Wed Nov 1 20:05:46 EDT 2017
Hi
The gate time on a 5335 can be set via GPIB. It can be set to some *very* long gates (well past 100 seconds).
When you do this, the data reported on GPIB does “stretch” to cover the added digits. The problem is that there
are internal register overflows. The designers did not anticipate needing quite so many bits. You loose the MSB’s
when you go to long gates. Compensating for this on a reasonable source is not a big deal.
Bob
> On Nov 1, 2017, at 6:14 PM, Dr. Frank <frank.stellmach at freenet.de> wrote:
>
>> I have an HP 5335A and I am measuring the output of a Suzler 2.5. I >have a GPSDO 10 MHz input into the back of the 5335A. >There is
> mention in the manual that the counter can display 11 or 12 >digits (in addition to the two Exponent digits). I presently have it >displaying nine digits. >Does anyone have one of these and could help me figure out how to get 12 >digits displayed? The manual is not very helpful here. >Richard
>
> Dear Richard,
>
> the maximum resolution are 11 siginificant digits on the display. That means, a leading '1' would then be the 12th digit. A leading 9 would give 11 digits. Over GPIB, I think, it's always formatted to 9 significant digits.
>
> The counter internally does not crop the result, but there's no way to output this "infinite" resolution over the bus, nor to read the internal counting and interpolation registers.
>
> Anyhow, you'll get 10 digits with 10 sec Gate Time, and the maximum of 11 digits with > 100 sec gate time.
>
> As the resolution is around 1ns / sec gate Time, maybe a bit lower than that, it's useful to have slightly longer gate Times, like 12 sec or 150 sec, to achieve this display resolution.
>
> There are two ways.
>
> At first, I replaced the 10µF tantalum capacitor C36 on A4 main board, which controls the long gate time, with a higher one, I think a 100 or 150µF Elco. That gave 12.5 sec maximum, and 10 digits.
>
> Then you might also use the manual gate control and a stopwatch, to have > 100sec gate time, and 11 digits.
>
> That might also work under GPIB control, commands GO and GC, but you get no GPIB readback, either.
>
> If you want to characterize your Sulzer vs. GPSDO, I would instead recommend Timelab (supports the 5335A) for the case of mid-to-longterm time constants, but GPSDO is not able to catch the short term stability of the Sulzer.
>
> Frank
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