Does a coil also have a capaciotance?
Joe Snodgrass
It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.
Artemus
"Joe Snodgrass" <joe....@yahoo.com> wrote in message
news:83993d5a-0ef4-486a...@e35g2000yqc.googlegroups.com...
>
> It seems to go against everything they taught us in class, but the
> various turns are closely spaced conductors, separated by a dielectric
> layer, just like the plates of a capacitor. TIA.
Yes. Its referred to as distributed capacitance. It has resistance too.
Likewise capacitors have L & R too.
Welcome to the real world which they didn't teach you about.
Art
John Larkin
Absolutely. Always. Lots of coils are spec'd to have an SRF,
self-resonant frequency. The impedance peaks at the SRF, and drops
above that frequency as the capacitance starts to dominate. Given SRF
and the inductance, you can calculate the equivalent capacitance, as
though all the C were connected to the ends of the inductor. Of
course, in real life the capacitance is distributed all over the
place.
The turns also have capacitance to the universe; and to the core, and
to other windings, if any.
John
Phil Allison
"Joe Snodgrass"
>
> It seems to go against everything they taught us in class, but the
> various turns are closely spaced conductors, separated by a dielectric
> layer, just like the plates of a capacitor.
** As others had said, any practical coil of wire has a self resonant
frequency due to it's capacitance. By measuring this frequency, one can find
the effective parallel capacitance - which may be from a few pF upwards.
Likewise, all practical capacitors have lead inductance and hence a self
resonant frequency - this time it's series resonance so the impedance value
drops to a minimum then rises. For most caps with wire leads each end, the
inductance is some value between 10nH and 40nH producing self resonant
frequencies of a few kHz to tens of MHz, depending on the cap value.
In both cases, the usual formula F = 1/( 2.pi. sq rt L.C ) applies.
.... Phil
Uwe Hercksen
Joe Snodgrass schrieb:
> It seems to go against everything they taught us in class, but the
> various turns are closely spaced conductors, separated by a dielectric
> layer, just like the plates of a capacitor. TIA.
Hello,
every real component has all three properties, resistance, inductance
and capacitance. There is no component with only one or two of these
properties.
Bye
Bill Sloman
Though you can often get away with ignoring the resistance of a super-
conducting inductor.
--
Bill Sloman, Nijmegen
Uwe Hercksen
Bill Sloman schrieb:
> Though you can often get away with ignoring the resistance of a super-
> conducting inductor.
Hello,
even in this case there is resistance, the isolation resistance of the
conductor to ground.
Bye
Phil Allison
"Uwe Hercksen"
>
> Bill Sloman schrieb:
>
>> Though you can often get away with ignoring the resistance of a super-
>> conducting inductor.
>
> conductor to ground.
** Hey Uwe,
Bill is Dutch and a colossal pedant.
But you sound like an much bigger, German one.
Show the old fool who is boss.
Go for it - boy.
.... Phil
Bill Sloman
> "Uwe Hercksen"
>
> >BillSlomanschrieb:
>
> >> Though you can often get away with ignoring the resistance of a super-
> >> conducting inductor.
>
> > even in this case there is resistance, the isolation resistance of the
> > conductor to ground.
>
> ** Hey Uwe,
>
> Bill is Dutch and a colossal pedant.
Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.
> But you sound like an much bigger, German one.
>
> Show the old fool who is boss.
>
> Go for it - boy.
Getting a Ph.D. is the kind of thing that instills pedantic habits -
but the comment about super-conducting inductors was made for comic,
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.
--
Bill Sloman, Nijmegen
John Larkin
That was comedy?
John
Bill Sloman
For those with the right kind of sense of humour - and it helps if you
didn't skip the relevant lectures back when you were an undergraduate.
--
Bill Sloman, Nijmegen
John Larkin
I doubt there were any lectures on superconductive inductors for me to
miss. And I rarely cut class.
I do work around superconductive magnets, well past $1e6 and 200
kgauss, in NMR and MRI and FTMS systems. They behave *almost* as
though they have zero resistance. Your statement somehow bypassed my
sense of humor.
How about you? Work with any interesting superconductor gadgets
lately?
John
Joel Koltner
news:83993d5a-0ef4-486a...@e35g2000yqc.googlegroups.com...
> various turns are closely spaced conductors, separated by a dielectric
> layer, just like the plates of a capacitor. TIA.
I don't think it really goes against everything they taught you in class, it's
more like they just might not have ever mentioned it explicitly. :-)
I do recall an exercise in an electromagnetics class where you determined the
capacitance of some coil so as to demonstrate that, at low frequencies, the
positive (inductive) reactance was a couple orders of magnitude higher than
the negative (capacitive) reactiance and hence could be ignored.
As others have mentioned, any arrangement of wires (and perhaps a dielectric)
will have all of resistance, capacitance, and inductance, but the goal is
usually to arrange them in a manner where one of these aspects dominates its
behavior, at least at the "frequencies of interest" where you intend to use
it. Dielectrics do play a large part in this too -- air core inductors are
much more commonly seen than air core capacitors, for instance (although this
is partially due to the fact that magnetic dielectric materials tend to have
non-negligible loss, hysteresis, etc. whereas there are a number of truly
excellent electric dielectric materials available than make for really good
capacitors).
---Joel
Bill Sloman
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 13 May 2011 09:11:15 -0700 (PDT),BillSloman
>
>
>
>
>
>
>
>
>
> <bill.slo...@ieee.org> wrote:
> >On May 13, 5:50 pm, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> >> On Fri, 13 May 2011 08:46:27 -0700 (PDT),BillSloman
>
> >> <bill.slo...@gmail.com> wrote:
> >> >On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
> >> >> "Uwe Hercksen"
>
> >> >> >BillSlomanschrieb:
>
> >> >> >> Though you can often get away with ignoring the resistance of a super-
> >> >> >> conducting inductor.
>
> >> >> > even in this case there is resistance, the isolation resistance of the
> >> >> > conductor to ground.
>
> >> >> ** Hey Uwe,
>
>
> >> >Actually I'm Australian (like Phil, though I don't take any pride in
> >> >him as a specimen of the Australian population) even if I'm currently
> >> >resident in the Netherlands.
>
> >> >> But you sound like an much bigger, German one.
>
> >> >> Show the old fool who is boss.
>
> >> >> Go for it - boy.
>
> >> >Getting a Ph.D. is the kind of thing that instills pedantic habits -
> >> >but the comment about super-conducting inductors was made for comic,
> >> >rather than pedantic effect, as someone with a more highly developed
> >> >theory of mind than Phil Allison might have been able to detect.
>
> >> That was comedy?
>
> >For those with the right kind of sense of humour - and it helps if you
> >didn't skip the relevant lectures back when you were an undergraduate.
>
> I doubt there were any lectures on superconductive inductors for me to
> miss. And I rarely cut class.
>
> I do work around superconductive magnets, well past $1e6 and 200
> kgauss, in NMR and MRI and FTMS systems. They behave *almost* as
> though they have zero resistance. Your statement somehow bypassed my
> sense of humor.
>
> How about you? Work with any interesting superconductor gadgets
> lately?
No. Did have an interesting conversation with a couple of guys at an
Analog Devices presentation earlier in the week - they are developing
an infra-red sensing array which basically runs on the edge of super-
conduction, with super-conducting quantum interference devices to
amplify the sensor output. The whole thing is going into a satellite
with a closed-circuit liquid helium refrigeration system.
I was deeply envious.
--
Bill Sloman, Nijmegen
Phil Hobbs
Superconducting bolometers are pretty amazing. At IBM a colleague of
mine had an FTIR spectrometer with one of those in it--it was better
than any available photodiode in the 3-5 um region.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
Phil Allison
"Bill Sloman = Lying Cunt"
"Phil Allison"
> "Uwe Hercksen"
>
> ** Hey Uwe,
>
> Bill is Dutch and a colossal pedant.
Actually I'm Australian
** Like hell.
You are a Dutch pig and massively autistic.
> But you sound like an much bigger, German one.
>
> Show the old fool who is boss.
>
> Go for it - boy.
Getting a Ph.D. is the kind of thing that instills pedantic habits
** Being a massive autistic fuckwit is the real reason.
FOAD you pathetic TROLL.
..... Phil
Spehro Pefhany
Some nasty vibrations from that cryocooler, I'll bet.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Michael A. Terrell
Phil Allison wrote:
>
> FOAD you pathetic TROLL.
Take your own advice, Phyllis.
--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.
Bill Sloman
> "BillSloman= Lying Cunt"
> "Phil Allison"
>
> > "Uwe Hercksen"
>
> > ** Hey Uwe,
>
>
> Actually I'm Australian
>
> ** Like hell.
>
> You are a Dutch pig and massively autistic.
Phil's got his opinion, and the Australian government has another.
> > But you sound like an much bigger, German one.
>
> > Show the old fool who is boss.
>
> > Go for it - boy.
>
> Getting a Ph.D. is the kind of thing that instills pedantic habits
>
> ** Being a massive autistic fuckwit is the real reason.
According to the ever-reliable Phil.
--
Bill Sloman, Nijmegen
Jamie
this is where Self resonance frequency (SRF) comes into play. The
coil will actually resonate at a freq with out any help from external
caps.
Coil designers have to keep this in mind.
Jamie
Phil Allison
> "Phil Allison"
>
> > "Uwe Hercksen"
>
> > ** Hey Uwe,
>
> >Billis Dutch and a colossal pedant.
>
> Actually I'm Australian
>
> ** Like hell.
>
> You are a Dutch pig and massively autistic.
Phil's got his opinion,
** Bill Sloman is living in Nijmegen with all his rellies around and waiting
for him to die.
> Getting a Ph.D. is the kind of thing that instills pedantic habits
>
> ** Being a massive autistic fuckwit is the real reason.
According to the ever-reliable Phil.
Bill Sloman, Nijmegen
** See.
..... Phil
Michael A. Terrell
It's actually called: "Self Resonant Frequency (SRF)"
Bill Sloman
> "BillSloman= Lying Dutch Cunt"
>
> > "Phil Allison"
>
> > > "Uwe Hercksen"
>
> > > ** Hey Uwe,
>
>
> > Actually I'm Australian
>
> > ** Like hell.
>
> > You are a Dutch pig and massively autistic.
>
> Phil's got his opinion,
>
> for him to die.
In fact most of my relatives live in Sydney. I'm going to be there for
most of June, July and August. If my relatives are "waiting for me to
die" they aren't exactly sitting on their edge of their seats. My
mother has appreciably more money than I do and has made it to 93 so
far ....
Phil's address in Sydney has been published on the web. I should print
out a few of his more entertaining subject headings in large print and
glue them to his front door ... taking care to bring along my large ex-
Rugby-playing lawyer nephew in case Phil feels upset by bad language
on his front door.
> > Getting a Ph.D. is the kind of thing that instills pedantic habits
>
> > ** Being a massive autistic fuckwit is the real reason.
>
> According to the ever-reliable Phil.
>
> Bill Sloman, Nijmegen
>
> ** See.
Phil doesn't see much - does he - and remembers less.
--
Bill Sloman, Nijmegen
Phil Allison
>
>
> > ** Like hell.
>
> > You are a Dutch pig and massively autistic.
>
> Phil's got his opinion,
>
> **Bill Sloman is living in Nijmegen with all his rellies around and
> waiting
> for him to die.
In fact most of my relatives live in Sydney. I'm going to be there for
most of June, July and August.
Phil's address in Sydney has been published on the web. I should print
out a few of his more entertaining subject headings in large print and
glue them to his front door ... taking care to bring along my large ex-
Rugby-playing lawyer nephew in case Phil feels upset by bad language
on his front door.
** That is 100% a criminal threat - Bill.
Not the first one you have made either.
You show up and I will call the police and have you put in jail.
Send anyone to do your dirty work and I will put them in the ground.
... Phil
Okkim Atnarivik
: On Fri, 13 May 2011 12:04:32 -0700 (PDT), the renowned Bill Sloman
: <bill....@gmail.com> wrote:
: >No. Did have an interesting conversation with a couple of guys at an
: >Analog Devices presentation earlier in the week - they are developing
: >an infra-red sensing array which basically runs on the edge of super-
: >conduction, with super-conducting quantum interference devices to
: >amplify the sensor output. The whole thing is going into a satellite
: >with a closed-circuit liquid helium refrigeration system.
: Some nasty vibrations from that cryocooler, I'll bet.
Sounds like the SAFARI instrument for the SPICA mission. Actually,
EMI causes more headache than mechanical vibrations, currently.
Regards,
Mikko
Robert Baer
1) Does a capacitor have inductance?
2) Does a 40 inch square, one inch long wire have capacitance? Inductance?
3) Does a sheet of glass have capacitance?
4) Explain your answers to all of the quesions above.
Okkim Atnarivik
To elaborate a bit: the final SQUID stage at 4K must drive several metres
of cable before there is the first location in the spacecraft with enough
cooling power to accommodate a decent semiconductor based amplifier. The 4K
cooling budget does not allow very much signal power to be generated there,
hence fighting to get enough SNR for the cable stretch with the presence of
EMI is indeed a headache. I have been considering a 4K amplifier operating
more deeply in D-class, or something with higher efficiency than a standard
SQUID anyway. An intersting twitch is that the standard SQUID in a way
*does* resemble the D-class amplifiers: the signal is effectively pulse
width modulated Josephson oscillation.
However, the schedule is so tight that there is not much opportunity to
develop anything novel or unproven, so perhaps we'll go by the brute force
and just shave the margins where-ever possible. A D-class CMOS amplifier
*might* do the job, but the handful off-the-shelf micropower CMOS comparators
I tried failed a quick test at 4K. A test would require a full custom chip
design it seems.
Regards,
Mikko
Spehro Pefhany
Did you end up using the SiGe option?
George Herold
<Okkim.Atnari...@twentyfour.fi.invalid> wrote:
> In sci.electronics.design Okkim Atnarivik <Okkim.Atnari...@twenrtyfour.fi.invalid> wrote:
> : In sci.electronics.design Spehro Pefhany <speffS...@interlogdotyou.knowwhat> wrote:
> : : On Fri, 13 May 2011 12:04:32 -0700 (PDT), the renowned Bill Sloman: : <bill.slo...@gmail.com> wrote:
>
> : : >No. Did have an interesting conversation with a couple of guys at an
> : : >Analog Devices presentation earlier in the week - they are developing
> : : >an infra-red sensing array which basically runs on the edge of super-
> : : >conduction, with super-conducting quantum interference devices to
> : : >amplify the sensor output. The whole thing is going into a satellite
> : : >with a closed-circuit liquid helium refrigeration system.
>
> : : Some nasty vibrations from that cryocooler, I'll bet.
>
> : Sounds like the SAFARI instrument for the SPICA mission. Actually,
> : EMI causes more headache than mechanical vibrations, currently.
>
> To elaborate a bit: the final SQUID stage at 4K must drive several metres
> of cable before there is the first location in the spacecraft with enough
> cooling power to accommodate a decent semiconductor based amplifier. The 4K
> cooling budget does not allow very much signal power to be generated there,
> hence fighting to get enough SNR for the cable stretch with the presence of
> EMI is indeed a headache. I have been considering a 4K amplifier operating
> more deeply in D-class, or something with higher efficiency than a standard
> SQUID anyway. An intersting twitch is that the standard SQUID in a way
> *does* resemble the D-class amplifiers: the signal is effectively pulse
> width modulated Josephson oscillation.
By EMI I assume you are talking about 'cr@p' leaking in through the
cable shield.
This is probably silly, but could an active shield driven from the
high temperature end help with EMI? I was playing around with a
driven shield last year to help get the signal out. (reduce cable
capacitance) So shield was driven by the signal. To shield from EMI
can you drive the shield with a signal from the outside? Some sort of
antenna? SQUIDS are pretty high frequency though, I was only doing
1MHz stuff.
George H.
Paul Hovnanian P.E.
[snip]
>
> That was comedy?
Yes. In the fine tradition going all the way back to Sophocles.
--
Paul Hovnanian mailto:Pa...@Hovnanian.com
------------------------------------------------------------------
Human beings were created by water to transport it uphill.
Okkim Atnarivik
SiGe is the obvious choice for the cryogenic LNA at the 'warm' 110K
end of the cable, but its efficiency when operated class-A causes too
much dissipation at 4K. Making a class-B or class-D amplifier out
of packaged SiGe discretes is probably too tedious, especially dealing
with the stability issues and the dissipation budget when there are many
active devices per an amp. Custom transistors or an ASIC would be
conceivable, e.g. SiGe devices from the AMS SiGe BiCMOS process (available
via MOSIS or Europractice) are known to function at 4K. Weinreb and his
colleagues have recently fabbed cryogenic SiGe amps for the SKA using
(I think) IBM SiGe process. A SiGe ASIC is probably a slow
path, however, which is likely to take several design iterations. We
have a superconducting foundry in-house, hence I'd prefer to keep the
control in our own hands and try to manage with SQUID-related devices.
Regards,
Mikko
Okkim Atnarivik
: By EMI I assume you are talking about 'cr@p' leaking in through the
: cable shield.
: This is probably silly, but could an active shield driven from the
: high temperature end help with EMI? I was playing around with a
: driven shield last year to help get the signal out. (reduce cable
: capacitance) So shield was driven by the signal. To shield from EMI
We did consider guarding, but that becomes tough at high frequencies
where the cable represents a (small) fraction of the wavelengths. Already a
small phase shift between the EMI and the guard signal would cause
untolerably strong coupling.
Regards,
Mikko