Return-Path: Received: from mail2.pe.net ([64.38.64.10]) by ns1.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-64832U3500L350S0V35) with ESMTP id com for ; Tue, 16 Jan 2001 19:30:39 -0500 Received: from ieee.org (IP-87-201.tem.pe.net [64.38.87.201]) by mail2.pe.net (8.9.3/8.9.1) with ESMTP id QAA19699 for ; Tue, 16 Jan 2001 16:39:00 -0800 (PST) Message-ID: <3A64E98E.DA909895@ieee.org> Date: Tue, 16 Jan 2001 16:38:38 -0800 From: "Charles R. Patton" Reply-To: charles.r.patton@ieee.org Reply-To: lancair.list@olsusa.com To: lancair.list@olsusa.com Subject: Re: Wet compass deflection References: X-Mailing-List: lancair.list@olsusa.com Mime-Version: 1.0 <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Carl, If the mu metal is close to the compass, then the magnet in the compass could be "attaching" to the mu muetal, i.e., the attraction of the compass magnet for the mu metal might be stronger than the field from the current in the wires you're trying to shield. That would become obvious when you swing the plane, the compass won't want to move. A thought would be to try and find a possible source by using a compass to move around the panel and look for the strongest reaction while the power is on. Is it the power wiring -- supply and return, or is it a piece of equipment, perhaps the power supply in a radio for instance? If it is the power wiring, one solution would be to try and minimize the loop area of the supply and return cabling. The larger this loop, the more likely the field will encompass the compass and cause a reaction. Another item to look at would be to think of the loop formed by the supply and return wiring and think of the imaginary plane it lies on in space. Twist that plane by adjusting the wire routing for minimum compass reaction. I.e., this is hard to explain, but I'm not saying totally reroute the power cabling, rather by 'twisting' the pair differently you can adjust the field at the compass to be vertical, thereby the compass will not react. Doing it this way, the amount of current won't matter, as you 'nulled' the field in relation to the compass. Charles R. Patton N360JM Carl Cadwell wrote: > In switching on the power, the wet compass swung 40 degrees. ... > The only solution that I came up with is a 6" x 6" mu metal sheet that > was placed under the glare shield and reduced the swing to 2-3 degrees > when the power is turned on. ... > Does anyone know if this is an acceptable solution? >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>