new usage for the nano question?

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dnordenberg
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new usage for the nano question?

Post by dnordenberg » Tue Aug 31, 2010 7:27 am

Hi

I was recently asked if I could locate the distance to a cable fault and I got the idea that the DSO nano could probably be used for this too with SING mode workning as requested to start with ;-)
The other thing that needs to be changed which might or might not be a easy task is to be able to send a single very short pulse with the test signal output.
The nano will trigger on the pulse sent out in SING mode and with the right time scale selected some echos should be visible on the screen. Echos will come from the wire end and/or at impedance changes troughtout the length of the cable. It should give you a picture of the quality of the whole cable length until the big echo comes from the cable end. By looking at this and measure the time (speed vary some with different cables, spec. often available from manufacturer) you could tell the distance to each fault or an open end.

Might be a good possible usage for the nano if it could be taught to send out single pulses?
PS. I know that there are expensive equipment available in stores that does this and which I have borrowed before but it was not the point with this post ;-)

Kind regards
David

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RoboKaren
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Re: new usage for the nano question?

Post by RoboKaren » Wed Sep 01, 2010 9:27 am

Sounds like a great idea!

I wonder how fast it would have to react.... so say you had a 50 meter cable with a break in it somewhere.... say at the 25 meter mark, then that would be 50 meters round trip for the pulse to go out and come back....

Let's assume that the pulse was travelling at near the speed of light (it slows down in copper, but I don't have that factor).... c = 299 792 458 m/s

So to travel 50 meters would be..... 50 / 299 792 458 = 1.66782048 × 10-7 sec

or 0.16 microsecond.......

That seems to me that you would need a processor that is sampling at the gigahertz range. So too fast for the little CPU in the Nano V2 to capture as an echo.


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That being said, there is another way to do it and that would be to use a beat oscillator to create an interference pattern that you can measure more easily. This is what high-end DGPS units use to get centimeter accuracy.

But I think it's beyond the skills of most DIY.... although people on this forum always surprise me!

Karen

dnordenberg
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Re: new usage for the nano question?

Post by dnordenberg » Thu Sep 02, 2010 11:40 pm

Hi

I did some calculations myself afterwards and realized this too :( 20MHz would get you quite far I think if you don't need need meter precision. I was thinking of cables in km length firstly in my usage but of course it would be cool to measure shorter stuff like ethernet cables too.

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