nuckolls.bob(at)aeroelect
Guest
|
 Posted: Sat Apr 23, 2011 9:38 am Post subject: Shielding |
 |
|
At 06:04 AM 4/23/2011, you wrote:
| Quote: | --> AeroElectric-List message posted by: dfritzj <dfritzj(at)yahoo.com>
Isn't shielded wire supposed to keep the noise off communication lines..... |
Sorta . . .
I'll refer you to chapter 16 on noise but in a nutshell . . .
While the term "noise" usually conjures up an image
of un-useful things heard in the headphones, audible
interference is but a small subset of antagonistic
stimulus finding its way into a potentially vulnerable
victims.
Not all things electrically 'wiggly' are noise. A
a potentially antagonistic stimulus does not become
noise until a potential victim is sufficiently
influenced by it that performance is unacceptable.
This is why the chapter on 'noise' is entitled
"Electromagnetic Compatibility". The broader
spectrum of examples for 'noise' might include
instruments that don't quite read right, ignition
systems that "mis", panel lights that flicker, etc.
Further, just because an airplane is carrying around
one or more potential antagonists and perhaps a handful
of potential victims is not an automatic recipe for
failure.
The noise must have a propagation mode. It can be
directly connected (trash on the power supply,
ground loop, etc), radiated (ammeter lays over
by radio energy from transmitter), capacitively
coupled (high voltage, spikey waveforms couple
to parallel wires in the bundle), and inductively
(high current, spikey waveforms couple to parallel
wires).
Of the four modes cited, capacitive and inductive
coupling are the weakest. I've never fixed a noise
problem in a system by adding shield. I've encountered
magnetically coupled noises three times I can recall.
Once on a Beechjet, once on a Hawker 800 and once
on my Plymouth Voyager. The rest of my ventures into
the dragon's lair were to find and sometimes fix
conducted and radiated propagation issues.
But know that for the kinds of potential
noises and the manner in which our itty-bitty
airplanes are built, shielding is the very
least of your worries. Follow manufacturer's
instructions. If a noise problem emerges,
the last portal to open to the dragon's lair
will be that of shielding.
Bob . . .
is the weakest and least
Bob . . . [quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
