X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 01 Jan 2010 10:32:57 -0500 Message-ID: X-Original-Return-Path: Received: from fmailhost03.isp.att.net ([207.115.11.53] verified) by logan.com (CommuniGate Pro SMTP 5.3.0) with ESMTP id 4053764 for lml@lancaironline.net; Wed, 30 Dec 2009 19:01:32 -0500 Received-SPF: none receiver=logan.com; client-ip=207.115.11.53; envelope-from=bbradburry@bellsouth.net Received: from desktop (adsl-146-123-245.mco.bellsouth.net[72.146.123.245]) by isp.att.net (frfwmhc03) with SMTP id <20091231000056H03000rdije>; Thu, 31 Dec 2009 00:00:57 +0000 X-Originating-IP: [72.146.123.245] From: "Bill Bradburry" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Re: Fuel Planning X-Original-Date: Wed, 30 Dec 2009 19:00:59 -0500 X-Original-Message-ID: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001F_01CA8982.6CF7BF90" X-Mailer: Microsoft Office Outlook 11 Thread-Index: AcqJojA1KIGCdmrVRICWQpPTUzRgPgACau+Q X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6001.18049 This is a multi-part message in MIME format. ------=_NextPart_000_001F_01CA8982.6CF7BF90 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Gary, If water would cause a large error, what would happen if gasohol was used and being hygroscopic, had water in it? For that matter, what if the sensor was calibrated with gasoline and then gasohol was used? Bill B _____ From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Gary Casey Sent: Wednesday, December 30, 2009 5:48 PM To: lml@lancaironline.net Subject: [LML] Re: Fuel Planning Just a quick note about the fuel level sensors: For a number of years I was responsible for the design an manufacture of capacitive level sensor, sold to all kinds of customers - except aerospace. I thought we could manufacture probes for experimental aircraft, so I took one from my ES kit and had it reverse engineered. We were surprised(shocked?) with what we found. The sensor is nothing more than an oscillator using the capacitance as the variable element. The only active element was a "555", probably the oldest and cheapest oscillator chip. There was no protection against moisture or contamination and no output protection (reverse or over-voltage, EMI, etc). There was no shielding against stray capacitance, a big issue with this type of sensor. No compensation for temperature effects (temperature variations are due more to the electronics than the fuel) or linearity errors. The outer shell is connected to "chassis ground", not the best approach. In fact, I use the outer shell as a ground for my fuel cap. Even with all those potential problems, the sensors work quite well. They are attached to a non-conductive housing, the electronics are enclosed in a reasonably dry, benign location, and most importantly, the customer is expected to calibrate each probe individually and take out all the offset, gain and linearity errors. We concluded that if we were going to enter the market we would incorporate all of our design features and probably couldn't be cost competitive in a very limited market that may not value the improvements. We dropped the project, and I instructed Purchasing to buy me a replacement sensor from EI. Turned out they smelled a rat and refused to sell one to what they must have thought was a competitor, thinking we were using it for reverse engineering. Duh. Several phone calls later I got my sensor. Conclusion is that even though these sensors may be light years better than the old resistive sensors, they are not perfect and not infallible. For instance, a slight amount of dissolved water (yes, gasoline will retain trace amounts of water) can have a big effect. 1% water will create a reading 40% high. They are simple, reliable and reasonably accurate devices - but not to be trusted with your life. Just my conclusions, for what they're worth. Gary Casey ------=_NextPart_000_001F_01CA8982.6CF7BF90 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Gary,

If water would cause a large error, what would happen if gasohol = was used and being hygroscopic, had water in it?  For that matter, what = if the sensor was calibrated with gasoline and then gasohol was = used?

 

Bill B

 

 

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Gary Casey
Sent: Wednesday, December = 30, 2009 5:48 PM
To: = lml@lancaironline.net
Subject: [LML] Re: Fuel = Planning

Just a quick note about the fuel level sensors:  For a = number of years I was responsible for the design an manufacture of capacitive = level sensor, sold to all kinds of customers - except aerospace.  I = thought we could manufacture probes for experimental aircraft, so I took one from = my ES kit and had it reverse engineered.  We were surprised(shocked?) = with what we found.  The sensor is nothing more than an oscillator using the capacitance as the variable element.  The only active element was a "555", probably the oldest and cheapest oscillator chip. =  There was no protection against moisture or contamination and no output = protection (reverse or over-voltage, EMI, etc).  There was no shielding = against stray capacitance, a big issue with this type of sensor.  No compensation = for temperature effects (temperature variations are due more to the = electronics than the fuel) or linearity errors.  The outer shell is connected = to "chassis ground", not the best approach.  In fact, I use = the outer shell as a ground for my fuel cap.  Even with all those = potential problems, the sensors work quite well.  They are attached to a non-conductive housing, the electronics are enclosed in a reasonably = dry, benign location, and most importantly, the customer is expected to = calibrate each probe individually and take out all the offset, gain and linearity = errors.  We concluded that if we were going to enter the market we would incorporate all of our design features and probably couldn't be cost competitive in a very limited market that may not value the = improvements.  We dropped the project, and I instructed Purchasing to buy me a replacement sensor from EI.  Turned out they smelled a rat and = refused to sell one to what they must have thought was a competitor, thinking we = were using it for reverse engineering.  Duh.  Several phone calls = later I got my sensor.

 

Conclusion is that even though these sensors may be light years = better than the old resistive sensors, they are not perfect and not infallible.  For instance, a slight amount of dissolved water (yes, gasoline = will retain trace amounts of water) can have a big effect.  1% water = will create a reading 40% high.  They are simple, reliable and = reasonably accurate devices - but not to be trusted with your = life.

 

Just my conclusions, for what they're = worth.

Gary Casey

 

 

 

------=_NextPart_000_001F_01CA8982.6CF7BF90--