I've seen similar results with my Racal-Dana 1992 counter. It has
trouble measuring time intervals when the inputs are almost in phase. I
think there has been discussion in the past about how various counters
handle that, but I can't find it right now.
Ed
On 5/1/2014 10:08 AM, Hans Holzach wrote:
with a teenage girl in the house it is easy to prefer macs over pcs...
unfortunately, Timelab does not work on my mac, but Plotter does (via
CrossOver).
however, if there is just a small number of data points per cycle,
Plotter will not remove the steps automatically, you have to do it
manually (that means Plotter removes only the step you mark). in my
example i had to remove 38 steps. i don't know the unwrapping
algorithm. it could indeed be a reason for the repeating pattern, but
certainly not the only one:
https://farm3.staticflickr.com/2937/13895219797_efd4ff07cd_o.png
when you look at the slope at the end of the cycle you see that the
slope is flat, it is even slightly positive, whereas at the beginning
of the new cycle it drops a bit sharper than for the rest of the
cycle. it looks like that at every step. in my opinion this is the
main reason for the repeating pattern, caused by the counter. removing
the step does not alter the last/first few data points of a cycle.
hans
What happens if you use Timelab to analyze the same data instead of
Plotter?
I find that, depending on the dataset, one program or the other will
sometimes have trouble removing the steps completely. They leave small
steps behind. It isn't related to the counter used, but seems to be
related to the number of data points per cycle and the unwrapping
algorithm used by the program.
Ed
On 5/1/2014 4:05 AM, Hans Holzach wrote:
> hi tom,
>
> thank you very much! that is quite interesting. i am happy to learn
> that there is nothing wrong with *my* counter! converting the
> non-linearity effect into a correction table is beyond my abilities,
> but simply knowing that this effect is inherent to the 53132a counter
> helps a lot.
>
> indeed, my plots look similar to yours. after only three hours of
> warming up i measured the TI of an HP 10811 against the 1 pps output
> of my fury. the 10 mhz output of the fury was used as the external
> timebase of the counter.
>
> the raw data of one hour measuring. average period of cycle wraps is
> 93.3 s:
> https://farm8.staticflickr.com/7314/14076566541_79094d6850_o.png
>
> steps and drift removed (detail):
> https://farm8.staticflickr.com/7348/14079753105_f8ac97766d_o.png
>
> autocorrelated. the average distance between two peaks is 94.6 s:
> https://farm6.staticflickr.com/5518/14056659576_703b446cc2_o.png
>
> as expected, the pattern is also visible in the ADEV plot
> (overlapping, all tau):
> https://farm8.staticflickr.com/7382/14079754735_62d70d1480_o.png
>
> and even better a few hours later (shorter period of cycle wraps):
> https://farm8.staticflickr.com/7042/14079754345_b4b6f9afb8_o.png
>
> but almost invisible in the "standard" ADEV plot:
> https://farm6.staticflickr.com/5474/13893141107_5aa39eb199_o.png
>
> hans
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