[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.
<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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