[time-nuts] HP 5335A Question
frank.stellmach at freenet.de
frank.stellmach at freenet.de
Thu Nov 2 08:20:07 EDT 2017
>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
Hi Bob,
You need to use timed GO and GC commands (Gate Open and Gate Close), for > 1sec Gate Time.
The GA command (Gate Adjust) is restricted from 1ms to 1 sec Gate time, so will not do the job.
See manual page 3-29.
One error correction: I replaced this 10µF Gate Time capacitor with a Tantalum type, 33µF, obviously, as these original 10µF already give about 4sec, so the 33µF are good for 12.5 sec, 10 digits.
The designers very well designed two near inifinite counter chains inside the 5335A.. I got my wisdom from the hp journal 9-1980.
They used a digital ASIC, called the MRC, multi-register counter, and it allows counting of the input signal and the time base, each 20 decades long. (see page 26).
Therefore, the Gate Time could be 300 000 years long, before an overflow from the 10MHz time base would occur, and the result would theoretically be precise to 20 digits resolution plus 2 digits for the time interpolator.
So you will NEVER loose any MSB information.
The GPIB output also does not stretch its resolution , because in the manual, they have a fixed digits output format.
On second read (pages 3-32 .. 3-34), it's not limited to 9 digits - sorry for the confusion - they reserve 14 digits for the mantissa, including sign and comma, so up to 12 digits can be transferred also, like on the display.. that means, also 11 significant digits over GPIB.
I assume, they internally use about 13 digits for the arithmetic routines, maybe taken over from the HP pocket calculators.
Frank
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