Return-Path: Sender: (Marvin Kaye) To: lml Date: Sun, 16 Mar 2003 09:19:43 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m08.mx.aol.com ([64.12.136.163] verified) by logan.com (CommuniGate Pro SMTP 4.0.6) with ESMTP id 2054082 for lml@lancaironline.net; Sat, 15 Mar 2003 23:12:22 -0500 Received: from Sky2high@aol.com by imo-m08.mx.aol.com (mail_out_v34.21.) id q.1e9.44d8f9e (4320); Sat, 15 Mar 2003 23:12:20 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <1e9.44d8f9e.2ba553a3@aol.com> X-Original-Date: Sat, 15 Mar 2003 23:12:19 EST Subject: Re: [LML] temperature probes X-Original-To: lml@lancaironline.net X-Original-CC: Cozyone2@aol.com MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_1e9.44d8f9e.2ba553a3_boundary" X-Mailer: 8.0 for Windows sub 840 --part1_1e9.44d8f9e.2ba553a3_boundary Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable In a message dated 3/15/2003 8:39:10 PM Central Standard Time,=20 glcasey@adelphia.net writes: > I have taken apart a Vision fuel probe and was amazed to > find that there was no, and I mean none, EMI protection built into the > circuitry, so that might give one a clue about the protection, or lack > thereof in the rest of the system. Gary, I also have the VM fuel probes - Exceptionally accurate and unaffected by=20 EMI/RFI. The probes send a digital frequency as a consequence of the=20 resistance/capacitance circuit at the probe. This differs from the=20 thermocouples that send a small voltage variation to an analog to digital=20 converter. These wires, carrying weak voltage signals, are susceptible to=20 RFI - thus disrupting the conversion. Note that the Rocky Mountain=20 Instrument OAT thermister circuit is not affected. <> The version of EGT and CHT probes are special wires covered with a braid=20 which I believe is shielded by contact with the probe case/engine. <>=20 The VM EPI 800 displays and the VM1000 display is connected to the "computer= "=20 via ribbon cable which carries all display data and is picked off by the=20 proper device. I doubt that the display is the problem. I too find it hard to believe the cause is noise on the power lead. Other=20 functions could be affected. I remain puzzled why some of us have this problem while other VM=20 installations do not. Scott Krueger N92EX --part1_1e9.44d8f9e.2ba553a3_boundary Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable In a message dated 3/15/2003 8:39:10 PM Central Standa= rd Time, glcasey@adelphia.net writes:

I have taken apart a Vision fue= l probe and was amazed to
find that there was no, and I mean none, EMI protection built into the
circuitry, so that might give one a clue about the protection, or lack
thereof in the rest of the system.


Gary,

I also have the VM fuel probes - Exceptionally accurate and unaffected by EM= I/RFI.  The probes send a digital frequency as a consequence of the res= istance/capacitance circuit at the probe.  This differs from the thermo= couples that send a small voltage variation to an analog to digital converte= r.  These wires, carrying weak voltage signals, are susceptible to RFI=20= - thus disrupting the conversion.  Note that the Rocky Mountain Instrum= ent OAT thermister circuit is not affected.

<<Another thought is just to twist the thermocouple wire pairs along t= heir whole length to make a poor man's shielded wire.=A0>>

The version of EGT and CHT probes are special wires covered with a braid whi= ch I believe is shielded by contact with the probe case/engine.

<<Or it could be directly radiated through the face of the display int= o the box, as that is probably the least well protected part>>

The VM EPI 800 displays and the VM1000 display is connected to the "computer= " via ribbon cable which carries all display data and is picked off by the p= roper device.  I doubt that the display is the problem.

I too find it hard to believe the cause is noise on the power lead.  Ot= her functions could be affected.

I remain puzzled why some of us have this problem while other VM installatio= ns do not.

Scott Krueger
N92EX



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