[time-nuts] Question about an HP5370B TIC

Bob Smither smither at c-c-i.com
Sat Oct 1 22:55:50 UTC 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.


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

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