Re: Instead scopes

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
the TCL to the CTE of the plastic.

If the length only is constant, the TCL is increased, and for a short fat
coil it’s nearly doubled.

In the case of something like B&W Miniductor, which has fairly fine-pitched
turns held by a few small axial stringers, the plastic stretches the length
of the coil but leaves the radial expansion free.

Because both a and b enter in the denominator, it’s possible to choose
dimensions that make the TCL of a Miniductor or similar coil very nearly
zero.

A normal single layer coil has a TCL around +30 ppm. I’ve never measured
one as bad as +120.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics