Received-SPF: none
 receiver=logan.com; client-ip=206.18.177.52; envelope-from=rlwhite@comcast.net
Date: Sun, 4 Feb 2007 10:08:25 -0700
From: Bob White <rlwhite@comcast.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: wire routing
Message-Id: <20070204100825.a56cc71a.rlwhite@comcast.net>
In-Reply-To: <list-1809967@logan.com>
References: <list-1809967@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

A little clarification here.  If you have a wire carrying a DC or low
freq AC signal, the aluminum will not shield the resulting magnetic
field.  You will get some benefit at higher frequencies because the
induced currents in the aluminum create a magnetic field that
counteracts the magnetic field produced by the wire.  Coupling is poor
at lower frequencies so it isn't as effective.

Using any kind of magnetic shielding around the compass can cause
problems because it will effect the magnetic field seen by the compass.

John's original questions concerned separating the fuel injector wiring
from the compass and EGT probe wiring.  Good idea in both cases.  The
compass is detecting a very low magnetic field of about 1 gauss so it
doesn't take much to affect it.  The EGT probes are low impedance
devices, which is good, but they generate millivolt level signals so are
also sensitive to induced errors.  Better to keep the high current
EFI pulses as far away as possible.

Bob W.  

On Sun, 4 Feb 2007 01:09:03 EST
Lehanover@aol.com wrote:

>  
> In a message dated 2/3/2007 11:56:08 P.M. Eastern Standard Time,  
> jwvoto@itlnet.net writes:
> 
> Am I wrong, I believe that aluminum will not  shield magnetic flux, giving 
> only electrostatic shielding; only steel will  shield magnetic flux.
>  
> Wendell
> 
> 
> 
> Notice that your IF cans have aluminum all around?  Never seen an IF  can?
>  
> In the olden days radios had big vacuum tubes, and open core capacitors to  
> adjust tank circuits and control frequencies. The Inter-frequency  transformers 
> had to be shielded to control phasing and awful noise in the  output. Thus 
> the aluminum can shielding. Good for wave guides as well. 
>  
> Ferris metals concentrate flux fields (conduct flux lines well) and are  used 
> in the cores of transformers and solenoids.  
>  
> Lynn E. Hanover
> 


-- 
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
First Flight:  11/23/2006 7:50AM - 1.7 Hours Total Time
Cables for your rotary installation - http://www.roblinphoto.com/shop/