Altimeter

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04 Sep 2012 23:15 #23416 by xjn001
xjn001 created the topic: Altimeter
Can anyone tell me how the altimeter works? The needle moves with the change in weather , but what about the outer ring? Do you need to know the elevation? If so, where do you turn and set the outer dial? Thanks for any help.

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19 Sep 2012 16:44 #23577 by oldbanger71
oldbanger71 replied the topic:
To my general information, it works with bi-metal springs that expand or retract with hight . one sets the ring or lever, so the hand is equal to zero, on the beginning of the trip and then you see the rise or lowering in meters or feet at the end of your trip, that is the sense of it, but hard to say anything particular without pictures, Philipp

The more i know, the more i realize that i don't know enough.
812 310 121 S

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22 Oct 2012 21:00 #23740 by silverghost
silverghost replied the topic: Slight Correction
The Altimeter is basically just a simple pressure Barometer that is able to be zero calibrated for local current weather barometric pressure conditions .
The higher you travel the lower the atmospheric pressure.
In the Altimeter's sensor element is a small sealed airtight "can" capsule that is ribbed like a bellows.
Air pressure pushes on this can capsule and squeezes it and it crushes and gets smaller & thinner.
The lower to sea level you are the more this bellows "can" crushes and shrinks & gets smaller as the air pressure get higher.
When you travel to a higher altitude the can relaxes and grows larger with less pressure acting on it in the thinner lower pressure air.
One side of this can is fixed to the main case housing and the other side is connected by small linkage elements to the indicator needle. The sensor can pulls, or pushes on the interconnecting linkage and thus moves the indicator neele up or down. The needle also has a small coiled hairspring to re-set this indicator needle as air pressure changes lower.
There is also a larger bias spring that works along with the bellows "can" to accurately calibrate it for proper pressure readings.

All Altimeters must be manually re-set depending on the local weather's current atmospheric barometric pressure~~~ Before they will read the proper altitude correctly.

The bi-metalic springs mentioned above are used only to indicate temperature as one metal reacts in expansion at a different rate to temperature changes.
These metals are bonded together and cause a slight twist to indicate proper temperature readings.
Bi-metalic springs are Not used in most Altimeters.

I just had to update this thread to slightly correct it as to it's real proper opperation & sensor elemnts. I am a mechanical engineer & designer & i just could not resist <!-- s;-) --><img src="{SMILIES_PATH}/icon_wink.gif" alt=";-)" title="Wink" /><!-- s;-) -->
I have been restoring, repairing, cleaning, lubricating, and calibrating vintage auto & aircraft gauges of all types, as well as spring wound mechanical & electro-mechanical clocks for many decades for my own auto collections as well as for select friends.
Philipp~ I hope I did not step on your toes, & prior post above, too harshly~~~that was never my intent .

This email address is being protected from spambots. You need JavaScript enabled to view it. BRAD HUNTER Huntingdon Valley Pa/Ocean City NJ 215 947 4676 Engineer & RE Developer Brass & Classic Auto, Antique Boat, Mechanical Automatic Music Machine, & Jukebox Collector

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22 Oct 2012 22:20 #23742 by oldbanger71
oldbanger71 replied the topic:
Hi Brad, thank you for correct explanation. My habit is to say what i belive is right and thankfully, there are people who know better and share their knowledge. A day without learning something new, is a lost day. CORDially Philipp

The more i know, the more i realize that i don't know enough.
812 310 121 S

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23 Oct 2012 22:50 #23753 by xjn001
xjn001 replied the topic:

This is the altimeter I am using.

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23 Oct 2012 23:14 #23754 by silverghost
silverghost replied the topic:
Very cool altimeter gauge !

I would suspect the real reason for having an altimeter on your car's dash,"in the day", other than just curiously knowing how high you were going, was so that you the driver could actually adjust your engine's carb fuel/air mixture settings as the air & it's contained oxygen got thinner as you drove to higher, or got higher at lower altitudes.
This is exactly what is actually done with aircraft engines.
This constant fuel/air mixture adjstment would avoid an overly rich fuel/air mixture at very high altitudes; and an overly lean mixture at much lower altitudes which would effect engine performance, power, & possibly engine life.

Does anyone know if a fuel/air mixture vs. altitude chart was ever printed in the original factory owner's/operations manual of any ACD autos for use along with these Altimeter dash gauges ?

This email address is being protected from spambots. You need JavaScript enabled to view it. BRAD HUNTER Huntingdon Valley Pa/Ocean City NJ 215 947 4676 Engineer & RE Developer Brass & Classic Auto, Antique Boat, Mechanical Automatic Music Machine, & Jukebox Collector

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