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August 2016

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Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Wed, 10 Aug 2016 10:09:19 +0200
Content-Type:
text/plain
Parts/Attachments:
text/plain (168 lines)
Gosh, TN isn't declining as I thought. Your challenge seems to place in a
research  lab. When I ran into ssuch problems and the solution proposals
grew until I couldn't decide which one to test (as usual you are expected
to do the job over a night and with no money) then I use go back and ask
myself if there might be another concept. Background noise is a plague and
many a time nearly impossible to eliminate. Therefore I wonder if not the
cheaapest and fastest way is to modify the noise source. B&O had a similar
issue with their studio recorders. They eliminated the problem by
encapsulate the motor in my-metal. The S/N lowered by one magnitude.  Just
a thought. Labbing with various resistiviity stuff can be expensive a
case.../Inge

On 9 August 2016 at 17:11, Carl Van Wormer <[log in to unmask]>
wrote:

> The longer story is (feel free to ignore this if you don't care about the
> background details):
>
> My short term goal is to set up an experiment to see if a shield of
> intermediate resistance will address my present condition.  We all know
> that the major cause or problems is . . . solutions.
>
> The inherited problem system is used to transfer power (5W-10W) during
> Phase 1 of operation, and to transfer acoustic signals (Piezo pickup, 10kHz
> to 1MHz) daring Phase 2 of operation.  The 100 turn, 15mm diameter coils
> were mounted inside of ferrite cup-cores with a gap between the 2 halves of
> the cores.  One core-half was mounted in a fixed aluminum housing, while
> the other was mounted in an aluminum housing at the end of a rotating shaft
> (on axis) with a gap between the cores of about 1mm.
>
> I came in to solve a noise pickup problem on the received acoustic signal
> which was caused by a VFD motor speed controller.  The symptoms could be
> simulated on the bench by connecting a 3kHz, 5V signal generator square
> wave to the rotating housing.  In the classic “fix it, but don’t change
> hardly anything” request, I found that I could shield the receiving coil
> (inside the core) with some copper foil tape (leaving a gap to avoid the
> “shorted turn” effect).  This eliminated the effect of the capacitive
> coupling on my test bench.  During the implementation phase, I found that
> we still had some noise that was traced to the capacitive coupling on the
> rotating (source) side.  Since the coils were not differential (one end of
> each was connected to local ground), the asymmetrical coupling signal
> caused a current to flow in the transmitting coil that magnetically coupled
> to the receiving coil.  Adding a shield to the rotating coil addressed that
> noise injection method.  The system was pronounced “Good.”
>
> We have found that the Phase 1 power transfer efficiency is reduced in the
> shielded systems.  Eddy current losses in the shield seem to be the cause,
> so I’m looking for ways to reduce those losses in my environment.  Raising
> the resistance of the shield material seems to be a simple solution, as
> long as the resistance is low enough to provide effective shielding.
> Unfortunately, I’ve been unable to find some easy to acquire samples of
> various resistive sheets to play with.  I was hoping to do some easy
> experiments to see if my resistive based shielding approach stands up to my
> first set of experiments before I started the process of defining a
> material to be used.  I’ve found some conductive ABS filament (
> http://www.makergeeks.com/coabs3dfi10.html) that might work if I can find
> somebody to print a plate and a method to electrically connect to it, but I
> don’t know a local friend with a 3-d printer.
>
> I’m still hoping for the sample kit of sheets of various resistivity
> materials, but I haven’t found the right page in the Digi-Key catalog . . .
>
> Thanks for any suggestions,
> Carl
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Tuesday, August 09, 2016 5:55 AM
> To: [log in to unmask]
> Subject: Re: [TN] looking for medium resistance material
>
> There is just about every type of material with just the right properties
> you are looking for available as a 3d printing medium.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
> Sent: Tuesday, August 09, 2016 12:44 AM
> To: [log in to unmask]
> Subject: Re: [TN] looking for medium resistance material
>
> Very kind of you Inge, but this is not really my cup of tea these days. I
> am aware that there are a number of suppliers of carbon based inks and
> these can be tailored to produce desired sheet resistivity ranges. That
> sort of thing is widely used on flex circuits and additive (printed
> electronics) circuitry. I would think  internet searching should bring up a
> good candidate list of suppliers in a few iterations . There is cross over
> here to ESD protection products, so that would be a good search area also.
>
>   ---
> Regards
>
>
> Mike
>
> www.chrisfennerfund.org
> www.facebook.com/chrisfennerfund/
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> Sent: Sunday, August 7, 2016 10:37 AM
> To: [log in to unmask]
> Subject: Re: [TN] looking for medium resistance material
>
> Carl,
> when  I was active I used to contact  SemiAlloys. I needed certain
> resistivity in lids for resistivity pulsed current seam welding of small
> packages for missiles. We produced about 50,000  pcs from SemiAlloys with
> He/Kr10 exp -10 with succcess.  Mike Fenner has more to say , I think..
> They are  extremly nice to cooperate with. Mike as well, despite he is
> english.
>
> Semi Alloys Inc
>
> 888 S Columbus Ave
>
> Mount Vernon, NY 10550
>
> (914) 664-8318)
>
>
>
> Good Luck / Inge
>
>
> On 7 August 2016 at 05:40, Carl Van Wormer <[log in to unmask]>
> wrote:
>
> > I usually want my physical structural resistances to be as low as
> > possible
> > (conductors) or as high as possible (insulators).  Now I need an
> > intermediate resistance, probably in the range of 100 to 1000 Ohms per
> > square.  The application will be an electrostatic shield in an
> > alternating field, hopefully balancing magnetic heating losses against
> > capacitive shielding effectiveness.
> > I have never seen these materials offered from any of my normal
> > sources, but I’m sure that there is something out there that will
> > work.  It could be sheet materials, paints, or slightly conductive
> > epoxies, or something else I haven’t thought of.  Since there is a
> > very wide experience base on this site, I’m asking here first.
> > Any suggestions will be appreciated.
> >
> > Thanks,
> > Carl
> >
> >
> > ​​​​​
> >
> > Carl B. Van Wormer, P.E., AE7GD
> > Senior Hardware Engineer
> > Cipher Engineering LLC
> >     21195 NW Evergreen Pkwy Ste 209
> >     Hillsboro, OR  97124-7167
> >     503-617-7447x303
> >     [log in to unmask]<mailto:[log in to unmask]>
> > http://cipherengineering.com<http://cipherengineering.com/>
> >
> > This message may contain confidential and/or proprietary information,
> > and is intended for the person/entity to whom it was originally
> > addressed. Any use by others is strictly prohibited.  If I sent this
> > to you by mistake, please be nice and delete it, and then tell me of
> > my mistake so I can send it to the right person.
> >
> >
> >
>

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