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JOHN TIPTON
Joined: 17 Sep 2006
Posts: 239
Location: Torquay - England
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 Posted: Fri Jan 21, 2011 1:47 am Post subject: Twisted pairs |
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Generaly speaking: when are 'twisted pairs' required, and why ?
Best regards - John
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Fri Jan 21, 2011 6:53 am Post subject: Twisted pairs |
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At 04:43 AM 1/21/2011, you wrote:
| Quote: | | Generaly speaking: when are 'twisted pairs' required, and why ? |
Pairing two conductors effects very tight
coupling of the magnetic fields around current
carrying conductors. When one conductor is the
return path for current flow in the other
conductor, the two resulting fields are equal,
opposite and in intimate proximity to each
other thus canceling each other out. The
conductors can be simply parallel to each other
(hard to maintain in a wire bundle) or twisted
such that they cannot get separated.
The corollary accurately suggests that the
same pair of wires are just as vulnerable to
externally impressed magnetic fields. Suppose you
have an itty-bitty signal you want to carry
from one place to another. Suppose further
that the wires carrying that signal are to
be bundled with lots of other wires carrying
who knows what . . . and worse yet, SINGLE
wires with (at)#$(at)-ugly currents flowing in
them.
They physics of magnetic coupling for pairing
outbound and return paths for currents
COMBINED with the physics of electro-static
coupling (easily broken by shielding) makes
the shielded-twisted pair a very robust
guard against signal contamination.
But as I mentioned earlier this week, fast
rise antagonists are rare in airplanes and
electro-static coupling is weak. Hence,
shielding is not nearly the guardian of
signal purity as is pairing (or twisting)
of the two conductors. I suggested that
the simple twisting of potentially vulnerable
or antagonistic current paths was about 99%
of everything a system integrator could
ask for in terms of interference control.
Bob . . . [quote][b]
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james(at)etravel.org
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| Posted: Fri Jan 21, 2011 7:11 am Post subject: Twisted pairs |
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Another brilliant and succinct explanation! Thanks Bob.
do not archive
On 21 January 2011 13:49, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
[quote] At 04:43 AM 1/21/2011, you wrote:
| Quote: | | Generaly speaking: when are 'twisted pairs' required, and why ? |
Pairing two conductors effects very tight
coupling of the magnetic fields around current
carrying conductors. When one conductor is the
return path for current flow in the other
conductor, the two resulting fields are equal,
opposite and in intimate proximity to each
other thus canceling each other out. The
conductors can be simply parallel to each other
(hard to maintain in a wire bundle) or twisted
such that they cannot get separated.
The corollary accurately suggests that the
same pair of wires are just as vulnerable to
externally impressed magnetic fields. Suppose you
have an itty-bitty signal you want to carry
from one place to another. Suppose further
that the wires carrying that signal are to
be bundled with lots of other wires carrying
who knows what . . . and worse yet, SINGLE
wires with (at)#$(at)-ugly currents flowing in
them.
They physics of magnetic coupling for pairing
outbound and return paths for currents
COMBINED with the physics of electro-static
coupling (easily broken by shielding) makes
the shielded-twisted pair a very robust
guard against signal contamination.
But as I mentioned earlier this week, fast
rise antagonists are rare in airplanes and
electro-static coupling is weak. Hence,
shielding is not nearly the guardian of
signal purity as is pairing (or twisting)
of the two conductors. I suggested that
the simple twisting of potentially vulnerable
or antagonistic current paths was about 99%
of everything a system integrator could
ask for in terms of interference control.
Bob . . .
| Quote: |
ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
|
[b]
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brucebell74(at)sbcglobal.
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| Posted: Fri Jan 21, 2011 7:29 am Post subject: Twisted pairs |
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DO NOT ARCHIVE!
My 1949 A35 Bonanza has twisted pairs to the mag compass light. It is mounted on the windshield. Came out the factory door June 1948. Noted when replacing the windshield 47 years ago. BBB
From: Robert L. Nuckolls, III (nuckolls.bob(at)aeroelectric.com)
Sent: Friday, January 21, 2011 7:49 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: Twisted pairs
At 04:43 AM 1/21/2011, you wrote:
| Quote: | | Generaly speaking: when are 'twisted pairs' required, and why ? |
Pairing two conductors effects very tight
coupling of the magnetic fields around current
carrying conductors. When one conductor is the
return path for current flow in the other
conductor, the two resulting fields are equal,
opposite and in intimate proximity to each
other thus canceling each other out. The
conductors can be simply parallel to each other
(hard to maintain in a wire bundle) or twisted
such that they cannot get separated.
The corollary accurately suggests that the
same pair of wires are just as vulnerable to
externally impressed magnetic fields. Suppose you
have an itty-bitty signal you want to carry
from one place to another. Suppose further
that the wires carrying that signal are to
be bundled with lots of other wires carrying
who knows what . . . and worse yet, SINGLE
wires with (at)#$(at)-ugly currents flowing in
them.
They physics of magnetic coupling for pairing
outbound and return paths for currents
COMBINED with the physics of electro-static
coupling (easily broken by shielding) makes
the shielded-twisted pair a very robust
guard against signal contamination.
But as I mentioned earlier this week, fast
rise antagonists are rare in airplanes and
electro-static coupling is weak. Hence,
shielding is not nearly the guardian of
signal purity as is pairing (or twisting)
of the two conductors. I suggested that
the simple twisting of potentially vulnerable
or antagonistic current paths was about 99%
of everything a system integrator could
ask for in terms of interference control.
Bob . . . [quote]
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
[b]
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Jan 21, 2011 8:26 am Post subject: Twisted pairs |
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At 10:24 AM 1/21/2011, you wrote:
| Quote: | My 1949 A35 Bonanza has twisted pairs to the mag compass light. It
is mounted on the windshield. Came out the factory door June 1948.
Noted when replacing the windshield 47 years ago. BBB
|
Great observation! The compass is tasked with
aligning itself to Momma Earth's very weak
magnetic field. It doesn't take much interference
to generate significant error in the compass reading.
This is why each compass installation is individually
calibrated (swung). Further, the calibration is
accomplished with certain conditions noted and
placarded (like radios ON).
A single illumination conductor up to the compass has
significant potential for adding magnetic interference
to the compass reading when illumination is on. Further,
the magnitude of that error would run up and down
with panel light dimmer settings. I've suggested that
the builder could also used a shielded wire where
the inner conductor is power up and shield was power
down from the light. The vast majority of such installations
do use a twisted pair to accomplish the same
result.
Bob . . .
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raymondj(at)frontiernet.n
Guest
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| Posted: Fri Jan 21, 2011 1:44 pm Post subject: Twisted pairs |
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do not archive
FWIW, in all my years around marine compasses I've never seen an
illuminated one that didn't use a twisted pair for illumination.
Raymond Julian
Kettle River, MN
On 01/21/2011 09:24 AM, Bruce B. Bell wrote:
| Quote: | DO NOT ARCHIVE!
My 1949 A35 Bonanza has twisted pairs to the mag compass light. It is
mounted on the windshield. Came out the factory door June 1948. Noted
when replacing the windshield 47 years ago. BBB
*From:* Robert L. Nuckolls, III <mailto:nuckolls.bob(at)aeroelectric.com>
*Sent:* Friday, January 21, 2011 7:49 AM
*To:* aeroelectric-list(at)matronics.com
<mailto:aeroelectric-list(at)matronics.com>
*Subject:* Re: Twisted pairs
At 04:43 AM 1/21/2011, you wrote:
> Generaly speaking: when are 'twisted pairs' required, and why ?
Pairing two conductors effects very tight
coupling of the magnetic fields around current
carrying conductors. When one conductor is the
return path for current flow in the other
conductor, the two resulting fields are equal,
opposite and in intimate proximity to each
other thus canceling each other out. The
conductors can be simply parallel to each other
(hard to maintain in a wire bundle) or twisted
such that they cannot get separated.
The corollary accurately suggests that the
same pair of wires are just as vulnerable to
externally impressed magnetic fields. Suppose you
have an itty-bitty signal you want to carry
from one place to another. Suppose further
that the wires carrying that signal are to
be bundled with lots of other wires carrying
who knows what . . . and worse yet, SINGLE
wires with (at)#$(at)-ugly currents flowing in
them.
They physics of magnetic coupling for pairing
outbound and return paths for currents
COMBINED with the physics of electro-static
coupling (easily broken by shielding) makes
the shielded-twisted pair a very robust
guard against signal contamination.
But as I mentioned earlier this week, fast
rise antagonists are rare in airplanes and
electro-static coupling is weak. Hence,
shielding is not nearly the guardian of
signal purity as is pairing (or twisting)
of the two conductors. I suggested that
the simple twisting of potentially vulnerable
or antagonistic current paths was about 99%
of everything a system integrator could
ask for in terms of interference control.
Bob . . .
*
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
*
*
*
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