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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Garmin altitude problems
Date: Sun, 11 Aug 2024 13:26:43 -0400
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On 8/10/2024 8:38 PM, Jeff Liebermann wrote:
>  
> As I understand it, all aviation barometric altimeters are temperature
> compensated.  I would think the aviation temperature compensation for
> air density method is somewhat similar to a marine barometer:
> <https://www.faa.gov/air_traffic/publications/atpubs/aip_html/part2_enr_section_1.8.html>
> I couldn't find anything that shows how the various gears work and
> where the bi-metallic temperature compensator is located (because of
> numerous interruptions today).
I just opened up the wall mounted aneroid barometer here in my study, an 
antique I inherited. It's an extremely simple lever mechanism, no gears 
involved. The capsule pushes up or down on a long thin lever arm. The 
vertical motion of the lever's end is converted to a horizontal motion 
of a tall thin post, which anchors the end of the smallest roller-style 
chain I've ever seen, maybe 0.050" pitch. That wraps around the needle's 
pivot shaft.  Here's a photo:
https://www.flickr.com/photos/16972296@N08/53916400376/in/dateposted-public/ 
  (Sorry, the "tall thin post" is in shadow.)

The left end of the lever system is not a pivot point, but instead is a 
rather wide brass stamping. I'd think that part could be made bimetallic 
to provide temperature compensation.


-- 
- Frank Krygowski