Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (March 2010, week 1)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Sat, 6 Mar 2010 10:48:25 -0600
Reply-To:     Larry Alofs <lalofs@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@GMAIL.COM>
Subject:      Re: AIR FLOW METER
Comments: To: Tom Hargrave <thargrav@hiwaay.net>
In-Reply-To:  <003901cabd49$cb5862b0$62092810$@net>
Content-Type: text/plain; charset=ISO-8859-1

Two comments:

When the carbon gets worn enough to cause noticeable drivability problems, the fraction of its length that is worn thru is still rather small; it is far from a continuous gap in the resistive surface. Thus it may not disrupt the behaviour of a nearby portion of the surface very much.

The important property of the device is that it behave as a linear (I think) potentiometer. If you verify that it does so after shifting the ceramic board a little, there should be no problem functionally.

Larry A.

On Sat, Mar 6, 2010 at 10:26 AM, Tom Hargrave <thargrav@hiwaay.net> wrote: > OK, now we are getting into my long term manufacturing history. We used to > manufacture thick film hybrids for GTE and the resistors on the hybrids were > made the exact same way - with printed on ink, then we would trim the > resistors up to value with a laser. > > We used ink manufactured to different values, for example 100 ohm ink was > 100 ohm when printed in a square regardless of the size of the square. But > if you were to print a rectangle twice as long as it was wide the value > would be 200 ohm. Now let me explain. > > A square of 100 ohm resistor ink 1cm X 1cm will measure 100 ohms from one > connection edge to another. > > Now put two of these resistors in series, or print a patch 1cm wide by 2cm > long, and the resistance is now 200 ohms from connection edge to connection > edge. > > Now put two of these in parallel, or print a patch 2cm wide by 1cm long, and > the resistance is now 50 ohms from connection edge to connection edge. > > Now put four of these resistors in a series parallel circuit, or print a > patch 2cm wide by 2cm long, and the resistance is back to 100 ohms from > connection edge to connection edge. > > Now apply this to the carbon resistor in the AFM. The track worn across the > resistor disconnects part of the parallel resistance from the circuit and > the readings have to change! > > Thanks, > Tom Hargrave > 256-656-1924 > > Our Web Sites: > www.kegkits.com > www.stir-plate.com > www.andyshotsauce.com > > > -----Original Message----- > From: David Beierl [mailto:dbeierl@gmail.com] On Behalf Of David Beierl > Sent: Saturday, March 06, 2010 10:12 AM > To: Tom Hargrave > Cc: vanagon@GERRY.VANAGON.COM > Subject: RE: AIR FLOW METER > > At 10:40 AM 3/6/2010, Tom Hargrave wrote: >>The fact that the carbon resistor is laser trimmed is what I was eluding to >>when I stated that relocating the wiper isn't a 100% fix. The problem is >>that the missing carbon track across the carbon resistor changes the value >>all the way across the sweep even when you relocate the wiper. > > Dear Tom, > > I'd like to see that tested.  There has to be some reason that they > made the thing so elaborate, and I strongly suspect that it's to > reduce the sensitivity of the device to the precise tracking radius > of the wiper.  Remember that it's acting as a potentiometer and its > output is a smoothly varying voltage; but if you measure > wiper-to-ground resistance while moving the vane it varies all over > the place.  I wish I had one to do some measurements on.  My > impression is that the large carbon surface contributes comparatively > little to the resistance. > > Yours, > David > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.733 / Virus Database: 271.1.1/2725 - Release Date: 03/06/10 > 01:39:00 >


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.