Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 2 Sep 2024 22:32:15 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 191
Message-ID: <vb5edf$3100v$1@dont-email.me>
References: <je01dj177m9p0q25en4k2jm8u0bsj07t2j@4ax.com>
 <vaq1f2$jdj$1@dont-email.me>
 <vaq762$1ssg1$1@solani.org>
 <vb163a$1dt9b$1@dont-email.me>
 <0ns8djtqe7ct4k21h8ubnj944fonq9i0u0@4ax.com>
 <vb29rd$1isoo$1@dont-email.me>
 <l4h9djl9rg8qip36cq0luehvf8cqprklbt@4ax.com>
 <orh9dj1svvp2i1rnhbkt3266uovqotofi4@4ax.com>
 <bmn9djt23ns3akfnfjaltiehr3ccuotkcs@4ax.com>
 <6p8adjh4ief0cfk1ohc1i54t6tob41q6o6@4ax.com>
 <nbgbdjtdf30hje01rqq5v0tptvpkknikbn@4ax.com>
 <vb4le6$2t5h0$1@dont-email.me>
 <pjccdjlu3d9glr745kpbsq9u6a6dqa28r0@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Tue, 03 Sep 2024 00:32:15 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="60524a633fb1b136ec7fffdcc5616199";
	logging-data="3178527"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/QOdnHWTcJfdUDGbeZGWtY"
User-Agent: NewsTap/5.5 (iPhone/iPod Touch)
Cancel-Lock: sha1:S/ylRQX+SMagKdVyE/CsUsqKj5c=
	sha1:8LfJWQ3+20+YEs3EKlmmeQTCZyg=
Bytes: 9069

john larkin <jlarkin_highland_tech> 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!
> 
>> 
>> 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. 
>> 
>> That made it easy to make nice looking, high-Q coils for the inductance
>> range of interest.  Good Medicine. 
>> 
>> Cheers 
>> 
>> Phil Hobbs 
> 
> Coilcraft makes a bunch of bare-naked RF inductors.
> 
> We like this encapsulated part:
> 
> https://www.coilcraft.com/en-us/products/rf/air-core-inductors/midi-spring/1812sms/?skuId=26054|26274
> 
> What's surprising is that the "natural" tempco of a copper solenoid
> inductor runs around +120 ppm/degC, but this one is around +40. The
> plastic must compensate for the copper somehow.
> 
> 
> 
> 

Sounds awfully high. 

To about 1% accuracy (over most useful aspect ratios), the inductance of a
single-layer coil is 

L(uH) = a**2 n**2 /(9a + 10b), 

Where a is the mean radius and b is the overall length, both in inches. 

If the thermal expansion is unconstrained, a and b vary together, so the TC
of inductance of such a coil is the same as the CTE of copper, about 17
ppm/K. 

A solid plastic form is strong enough to stretch the copper and increase
========== REMAINDER OF ARTICLE TRUNCATED ==========