X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 10 Jun 2007 11:29:19 -0400 Message-ID: X-Original-Return-Path: Received: from global.delionsden.com ([66.150.29.112] verified) by logan.com (CommuniGate Pro SMTP 5.1.9) with ESMTPS id 2094377 for lml@lancaironline.net; Sun, 10 Jun 2007 03:29:19 -0400 Received-SPF: none receiver=logan.com; client-ip=66.150.29.112; envelope-from=n103md@yahoo.com Received: from bmackey by global.delionsden.com with local (Exim 4.62) (envelope-from ) id 1HxHqr-0008Pq-5M for lml@lancaironline.net; Sun, 10 Jun 2007 03:28:41 -0400 Received: from 69.12.132.145 ([69.12.132.145]) (SquirrelMail authenticated user bmackey) by www.bmackey.com with HTTP; Sun, 10 Jun 2007 00:28:41 -0700 (PDT) X-Original-Message-ID: <1364.69.12.132.145.1181460521.squirrel@www.bmackey.com> X-Original-Date: Sun, 10 Jun 2007 00:28:41 -0700 (PDT) Subject: Re: [LML] Unstable Fuel Quantity indication From: "bob mackey" X-Original-To: lml@lancaironline.net User-Agent: SquirrelMail/1.4.8 MIME-Version: 1.0 Content-Type: text/plain;charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - global.delionsden.com X-AntiAbuse: Original Domain - lancaironline.net X-AntiAbuse: Originator/Caller UID/GID - [32015 2012] / [47 12] X-AntiAbuse: Sender Address Domain - yahoo.com X-Source: X-Source-Args: X-Source-Dir: > I'm not an EE but the whole capacitive probe setup seems sketchy to me. > You have a 5v square wave signal coming from the sender with limited or > no shielding. In some cases the sender is connected to a freq->voltage > converter and then on to the engine monitor. The converter is a circuit > board in a plastic box with no shielding (and maybe no grounding) in my > case. In my day job, I work for a company that makes capacitive sensors. We make the sensors that detect your finger on a laptop touchpad, or cell phone, or music player. Properly designed, the sensors are very sensitive, resistant to RF interference, and almost indestructible. The plastic box with a F/V converter you described is very primitive by comparison with modern electronics. Sounds like the Heathkit version from the 1970's. A simple fuel level sensor uses a wire inside a tube. When the tube is full of fuel, the capacitance is greater than when it is full of air. The only moving part is the fuel itself. This coaxial part is very robust, and easy to electrically shield from interference. > EI says resistive probes wear out sooner but I wonder. > Seems like a more appropriate solution. The resistive probes that I have seen have a moving float connected to a potentiometer. The fact that it has moving parts exposes it to wear. The fact that it uses a sliding contact potentiometer means that it will wear out fairly soon. If there is enough demand, and a reasonably standard output format, I could make a circuit for measuring capacitance and reporting it to an MFD. With only a little more effort it could detect water or alcohol in the fuel and set an alarm. The size and weight would be negligible compared to the sensing tube. Who would know what output format would be appropriate?