[time-nuts] Question about an HP5370B TIC

Bob Smither smither at c-c-i.com
Sat Oct 1 18:55:50 EDT 2011


Hal Murray wrote:
>> If I put the 5370B in the +/-TI mode I expected to see both + and -  small
>> time differences when the two signals are closely aligned - and  mainly I
>> do.  Typically the difference is + or - a usec or less.  Occasionally
>> however the 5370B displays very near to a +1 or -1 second  (999.999 xxx ms
>> or -1.000 000 xxx s for example) reading.  Needless to  say this plays havoc
>> with trying to measure a mean value of the  alignment.  The 5370B is clearly
>> measuring the "outside" between the  pulse pair when I want it measure the
>> "inside" (or short time interval)  between the pulse pair.
> 
> How are you collecting the data?  If each sample gets to a PC, you can fix it 
> up in software.
>     If X > 0.5: X = X -1.0
>     If X < -0.5: X = X+1.0
> One disadvantage of that is that those samples eat 2 pairs of pulses so you 
> are only getting half as as many samples per hour.

I don't have it recording to a PC yet.  Actually, my order of GPIB 
cables came today!  I have an old ISA bus GPIB card, just need to get a 
minimal Linux install up and should be able to talk to the 5370B (and 
other instruments I have).

> I like John's suggestion of triggering one side off the other edge of the 
> pulse.

Yep.  See my other response.  That works fine for now.

> Is the pulse from the OCXO supposed to be synchronized with the GPS second?  
> If not, just zap the counter to move the pulse around within the one second 
> window.  (I'm thinking of shorting out one of the counter bits with a 
> screwdriver or clip lead for a fraction of a second.)

   :-).  I actually have a SPDT switch that I can move one of the 
counter decode taps with and slew the edge with some control.

<snip>

Thanks!
-- 
Bob Smither, PhD                                 Circuit Concepts, Inc.
=======================================================================
Blessed is he who expects no gratitude, for he shall not be
disappointed.
   -- W. C. Bennett
=======================================================================
Smither at C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)

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