[time-nuts] Newbie questions

[Bob Camp]

Hi

I agree with you on the spec sheet and the fact that the cpu *should* extend
the data. My observation was that it didn't do it if the input frequency was
high enough. I tried it on a couple dozen counters built over a period of
several years.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Magnus Danielson
Sent: Wednesday, January 06, 2010 12:10 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Newbie questions

Hi!

Bob Camp wrote:
> Hi
> 
> Ahhh, that jogs a few of the tired old brain cells....
> 
> You can run the gate off of the GPIB input to get all kinds of silly long
> gates. Then you start to get into the cpu overflow issues. Since it's a
MSB
> overflow you can usually clean it up in software *if* you know it's
> happening. 

Notice that it is specified to support gate-times up to 10 Ms (10^7 s). 
I would suspect that both the event and time counters is CPU extended.

Maybe I should pull the PROM and do a readout.

> Since the GPIB is simply telling the counter "start about now" and "finish
> it up now" the accuracy of the GPIB timing does not get into the result.
The
> counter still uses it's time base as the standard of comparison.

Well, it will cause a variation in gate-time (about 2 ms can be assumed, 
since that is what programmed gate using GA allows) , but since this is 
used for longer gate times it is not significant. If better precission 
is needed, the external arm input shall be used.

Cheers,
Magnus

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