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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Thu, 5 Sep 2024 16:54:47 +1000
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On 5/09/2024 12:50 am, john larkin wrote:
> On Tue, 3 Sep 2024 15:30:13 +1000, Bill Sloman <bill.sloman@ieee.org>
> wrote:
> 
>> On 3/09/2024 7:57 am, john larkin wrote:
>>> On Mon, 2 Sep 2024 15:25:59 -0000 (UTC), Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>>> On Sun, 01 Sep 2024 19:49:39 -0700, john larkin
>>>>> <jlarkin_highland_tech> wrote:
>>>>>
>>>>>> On Sun, 01 Sep 2024 17:43:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>> wrote:
>>>>>>
>>>>>>> On Sun, 01 Sep 2024 13:17:03 -0700, john larkin
>>>>>>> <jlarkin_highland_tech> wrote:
>>>>>>>
>>>>>>>> On Sun, 01 Sep 2024 15:53:46 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> On Sun, 1 Sep 2024 17:55:58 -0000 (UTC), Phil Hobbs
>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>>>
>>>>>>>>>> john larkin <jlarkin_highland_tech> wrote:
>>>>>>>>>>> On Sun, 1 Sep 2024 17:45:46 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> On 30/08/2024 2:21 am, Jan Panteltje wrote:
>>>>>>>>>>>>> On a sunny day (Fri, 30 Aug 2024 00:43:39 +1000) it happened Bill Sloman
>>>>>>>>>>>>> <bill.sloman@ieee.org> wrote in <vaq1f2$jdj$1@dont-email.me>:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> It's lot easier and quicker to bread-board a circuit in LTSpice than it
>>>>>>>>>>>>>> is to wire up a test circuit, but what that means is that you need to
>>>>>>>>>>>>>> make fewer real circuits and they are a lot more likely to work when tested.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> That, on it's own, is enough to explain why labs look different today
>>>>>>>>>>>>>> than they did in the dark ages.
>>>>>>>>>>>>>
>>>>>>>>>>>>> All it explains is boeings falling apart and astronuts ending up stuck at the ISS
>>>>>>>>>>>>> and no moonlanding from the US, not even a probe.
>>>>>>>>>>>>> Slimulations are _not_ realty and never will be.
>>>>>>>>>>>>
>>>>>>>>>>>> But they can capture useful parts of reality, if you know what you are
>>>>>>>>>>>> doing.
>>>>>>>>>>>>
>>>>>>>>>>>> John Larkin's simulated inductors tend not to have any parallel capacitance.
>>>>>>>>>>>
>>>>>>>>>>> The trick is to know when it matters. ESR and core loss are usually
>>>>>>>>>>> more important.
>>>>>>>>>>>
>>>>>>>>>>> I designed this surface-mount inductor for my Pockels Cell driver,
>>>>>>>>>>> after several tries using commercial parts. They all smoked.
>>>>>>>>>>>
>>>>>>>>>>> It's wound on a specially marked Sharpie pen that we have carefully
>>>>>>>>>>> reserved.
>>>>>>>>>>
>>>>>>>>>> It better have a regular calibration schedule, or your semiconductor
>>>>>>>>>> customers may give you the raised eyebrow.
>>>>>>>>>
>>>>>>>>> Hmm.  To be overly serious:  With traceability to NIST (US) or NPL
>>>>>>>>> (UK) or the like.
>>>>>>>>>
>>>>>>>>> The trend in standards is to eliminate standards tied to a physical
>>>>>>>>> object.
>>>>>>>>>
>>>>>>>>> I have a Sharpie in hand.  The barrel that is not covered by the cap
>>>>>>>>> is a truncated cone, being 11.0 mm at the blunt end and 12.32 mm near
>>>>>>>>> the cap, 73 mm away.
>>>>>>>>
>>>>>>>> Mine is pretty cylindrical for the length of the coil. I expect that
>>>>>>>> the operator's (ie, my)  applied tension affects the radius too.
>>>>>>>
>>>>>>> Most likely.
>>>>>>>
>>>>>>>
>>>>>>>> That inductor sees 25 amps p-p, roughly a sawtooth, at 4 MHz. The
>>>>>>>> Coilcraft parts that I tried all smoked, I guess from skin effect and
>>>>>>>> proximity effect.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Actually, all that's needed is to specify an ideal geometric shape,
>>>>>>>>> with tolerances, in the formal documentation.
>>>>>>>>>
>>>>>>>>> Joe Gwinn
>>>>>>>>
>>>>>>>> I'll have someone start on a SolidWorks model.
>>>>>>>
>>>>>>> I bet you need the standoff, so the lossy FR4 material isn't too
>>>>>>> close.  That should be in the requirements as well.
>>>>>>
>>>>>> The turns squish down into the gap-pad gunk, which is an OK heat
>>>>>> conductor. The PCB under the pad is a big copper pour, top and bottom,
>>>>>> with a zillion thermal vias.  There's more gap-pad on the underside of
>>>>>> the board to dump heat into the baseplate.
>>>>>>
>>>>>> At 4 MHz, skin depth is 32 microns, so most of the copper is wasted.
>>>>>> That's why it gets so hot.
>>>>>>
>>>>>> I tried three of the Coilcraft 1010VS parts in series, but they
>>>>>> smoked, probably skin+proximity effect.  Maybe parallel would have
>>>>>> been better.
>>>>>>
>>>>>>>
>>>>>>> I'd specify the coil dimensions, not the mandrel dimensions, which may
>>>>>>> be provided as a helpful suggestion only.
>>>>>>>
>>>>>>> Joe Gwinn
>>>>>>
>>>>>> I could have a mandrel machined or 3D printed, to more accurately wind
>>>>>> the inductor. The improvement would be mostly cosmetic.
>>>>>
>>>>> Or choose a 12mm OD mandrel, and adjust elsewhere.  The advantage of
>>>>> 12mm is that it's a common size. so just buy the rod and use it.
>>>>>
>>>>> .<https://www.mcmaster.com/products/shafts/shafts-2~/rotary-shafts-5/diameter~12-mm/>
>>>>>
>>>>> Actually, the requirement is a certain inductance while handling a
>>>>> 4-MHz sawtooth at 25 Amps (p-p), so the frequency band is roughly 4 to
>>>>> 20 MHz, to cover the first five harmonics  Which harmonic causes the
>>>>> most heating?
>>>>>
>>>>> The dimensions et al are the construction details needed for Highland
>>>>> to be able to replicate the part without your help.
>>>>>
>>>> Lo these forty year gone, I had this RF gig that involved making a lot of
>>>> VHF LC oscillatior and filter protos.
>>>
>>> I still design LC oscillators!
>>
>> You may put them together, but it sounds as if you evolve them rather
>> than design them. And you'd have your own coil-winding gear if you did
>> much of it. As Phil did.
> 
> Design, simulate, build, test, evolve. That's how engineering usually
> works.

Serious engineering goes more like design, simulate, redesign,simulate 
again, build, test, modify-evolve, retest, design, simulate, build, 
test, ship.

> At the bleeding edge of performance, unpredictable higher-order
> effects happen. 

As if you were ever there.

> Sometimes whacking the competition depends on
> understanding and taming those effects. That's more fun to me than
> pushing a bunch of equations around.

But if you don't push the equations around you don't get to understand 
the effects properly, no matter how proud you are of your "intuition".

>>>> We had a hand-cranked coil winder that had a good selection of cylindrical
>>>> steel mandrels with helical grooves to guide the wire, plus three or four
>>>> sheets with tables of measured values for single-layer coils of various
>>>> lengths.  With a couple of training runs, one learned how hard to pull on
>>>> the wire so that it would just spring free from the mandrel.
> 
> My Sharpie is a nice red marker when it's not winding coils.

But it is still a ppor excuse for a coilwinder.

>>>> That made it easy to make nice looking, high-Q coils for the inductance
>>>> range of interest.  Good Medicine.
>>
>> At George Kent in Luton (1973-76) I got to wind my own small-signal
>> transformers. At Cambridge Instruments (1982-1991) I had to ask the
>> coil-winders on the shop floor to do it for me.
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