[time-nuts] Dana Racal 1996 Questions

Ulrich Bangert df6jb at ulrich-bangert.de
Sat Mar 3 06:14:30 EST 2007


I own a 1996 since 20 years and use it on a regular base. Mine will give
a wrong measurement result from time to time. May run flawlessly for
hours and then give one complete false reading. May be software, may be
hardware. Remember the electrolytic capacitors in it may be 30 or more
years old, having most probably lost some of their capacitance. I can
well imagine that the device reacts today more sensitive to anything on
the power line than when it was young.

Regarding the second part of your question: Imagine the 1996 basically
as a time interval counter about which Racal Dana claimed that is has an
single shot resolution of 1 ns. The 1 ns is a bit conservative. If one
dives deeper into measurements with the 1996 and gets the COMPLETE
results over the GPIB (which has more digits than you see in the
display) then it becomes more likely that the true single shot reolution
may be in the order of 300-400 ps but with an estimatiom of 1 ns you are
on the safe side. Since the 1996 is intelligent, every measurement that
it makes, regardless of being frequency, time intervall or phase can be
reduced to an time interval measurement for wich the counter has a
certain time availabale, i.e. app. the gate time you set it. If you
apply the 1 ns absolute resolution to the measurement time availabale
you come to a relative resolution of 1E-9 @ 1 s gate time, 1E-10 @ 10 s
gate time and 1E-11 @ 100 s gate time. Up to that it is physiscs and
electronics that increase the relative resolution. You may apply
additional mathematics to your measurements but that will not increase
the physical measurement resolution.

Since the 1996 will always try to give you the full available accuracy
and resolution of an result, there are chances that the 10 digit display
is not adequate to display all significant digits. In this case the 1996
"overflows" which is by no means an indication for an error but simply
for the fact that not all of the digits are displayed (while they are on
the GPIB). In this case the "O/F" led will turn on and indicate that the
number displayed has 1 or 2 digits left of the most significant
displayed digit that are not to be seen. However the missing digit(s)
are easily guessed: With 10 MHz applied and a display of

0.000000001 E 6 

the missing digit is clearly a "1" while in the same situation an

99.99999999 E3

clearly shows that there must be two "9"s that we are missing.

Best ragards
Ulrich Bangert, DF6JB   

> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von tom jones
> Gesendet: Samstag, 3. März 2007 02:39
> An: time-nuts at febo.com
> Betreff: [time-nuts] Dana Racal 1996 Questions
> 
> 
> Anybody using either 1996 or 1995 racal counters.
>   I use my hp5061a for external reference to both counters
>   The racals are continously in mean average mode (10000 
> seconds).with a different 
>   1pps signals to the racal counters.. 
>   Occasionaly the counters present a reading like 10.0  -3 (10ms)
>   The expected readings should be 0.001 -9   (1ps)
>    
>   Anybody else using dana racal experience this. It seems 
> like a software bug?
>    
>   Question number two;
>                 The readings from these racals seem off .
>   I get a reading like 0.001 -9  equals 1X10 -12  I belive 
> its decimal point mighy be off.
>   I'm thinking it should be  .0001 -9 equaling 1X10-13  When 
> I interpet the readings with the extra digit of accuracy the 
> readings make more sense and correlate with my austorn loran 
> frequency & timing receivers and other counters and gps 1pps signals.
>    
>   To also support my theory  the racal counters will resolve 
> 1X10 -11  using 99 (100s)  second gate time. when I activate 
> the mean average mode this extends the gate time two more 
> decimal places (10000 second gate) wouldn't you assume a 
> resultt of 2 more digits in accuracy ?  
>          
>    
>    
> 
>  
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