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clipping a fast negative pulse

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T3sl4co1l:

--- Quote from: AndyC_772 on May 10, 2019, 04:01:29 pm ---
--- Quote from: brumbarchris on May 09, 2019, 08:24:29 pm ---
--- Quote ---Wait.  Why are you clipping the pulse you fought so hard to perfect?
--- End quote ---

In order to further signal process it and feed it to an ADC eventually.

--- End quote ---

Hang on... what?? You want to precisely clip a signal which is going to be digitised?

In that case, your clipping 'circuit' is two lines of code:


--- Code: ---for (i = 0; i < SAMPLE_BLOCK_SIZE; i++)
  sample_data[i] = (sample_data[i] < CLIP_LEVEL) ? CLIP_LEVEL : sample_data[i];

--- End code ---

--- End quote ---

Analog clipping is probably still required to protect voltage ranges, but in the end, digital will be far more accurate than anything else.  ADCs don't usually suffer from recovery effects either, so the saturation (to 0x000 / 0xfff) can be used implicitly as well (but, that may be something to test; ADCs fail in all sorts of fascinating ways).


It bears noting that the abstraction process only works if the one doing the abstraction, fully understands the specifications of the systems above and below the abstraction interface.  This exercise strikes me as an overzealous (and perhaps inexperienced?) abstraction, that would benefit more from a holistic design process instead.

That just leaves one thing --


--- Quote from: brumbarchris on May 10, 2019, 08:17:10 am ---Well, we have to build and extend whatever experience already exists within our company (not much, admittedly, but more than nothing with regards to the pulse induction principle).

--- End quote ---

-- the force of "not invented here".  Even when the existing background is sparse, there is a strong tendency to stick to what is "known", even if very little is actually known.


--- Quote from: Kalvin on May 10, 2019, 08:55:13 am ---It is funny how these toy metal-detectors are still developed and manufactured. Is this due to the lack of competition or what?

--- End quote ---

Beats me -- they're definitely out there.  Last time I saw an eddy current analyzer at work, it was being used to check the martensite fraction (and to what depth) of an induction-hardened steel workpiece.  A subtle application, but apparently representative and repeatable enough to work.  Not that I can recommend anyone just go out and buy an industrial eddy current analyzer for any generic purpose (guessing they're in the $10k price range, as much industrial kit is), but the basic idea in any case is quite tractable, and simplified versions are available for peanuts (like metal detectors) that arguably could be used for the core functionality, and hacked to the OP's goal, without having to invent anything new. :)

Tim

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