[time-nuts] HP 5335A Question

Dr. Frank frank.stellmach at freenet.de
Wed Nov 1 18:14:45 EDT 2017

>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. 

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.


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