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'Air pressure'
1999\05\04@233314 by

The discussusions on the pitot tube remindes me of a project I had on
the back burner and some questions I had about it.  I wanted to build a
PIC based variometer(displays vertical speed based on rate of air
pressure changes).  Does anyone have the formula for converting the rate
of pressure change to vertical speed?  Has anyone out there done this
before?

Yes this sort of thing has been done.
This (actually a derivative of it) is what rekindled my interest in microcontrollers.

In model rocketry there are several folks building their own (or purchasing) altimeters which run on the barometric air pressure. The equations are fairly straight forward HOWEVER they are  logarithimic..... best accomplished through lookup tables.

email me and I can send you the URL for a few designs.
Similarly, there is a guy running a project on a portable avionics package/platform which shows a lot of promise.

Des

>>> Brian Kraut <engaltEARTHLINK.NET> 5/5/99 4:34:44 pm >>>
The discussusions on the pitot tube remindes me of a project I had on
the back burner and some questions I had about it.  I wanted to build a
PIC based variometer(displays vertical speed based on rate of air
pressure changes).  Does anyone have the formula for converting the rate
of pressure change to vertical speed?  Has anyone out there done this
before?

Another basic principle is to have a tank - as large as possible - and look at the air-flow out of it (ascending) or into (descending). Most likely too bulky for a small airborne gadget.  :=)

Sven
-----Ursprungligt meddelande-----
FrŒn: Des Bromilow <Des.BromilowCITEC.COM.AU>
Till: PICLISTMITVMA.MIT.EDU <PICLISTMITVMA.MIT.EDU>
Datum: den 5 maj 1999 06:32
€mne: Re: Air pressure

{Quote hidden}

MILTON MEDICINTEKNIK KB wrote:

> Another basic principle is to have a tank - as large as possible - and
> look at the air-flow out of it (ascending) or into (descending).

I remember that one from 20++ years ago, for gliders.  Two thermistors
(bolometers) back-to-back on a strut across the nozzle to the tank.

> Most likely too bulky for a small airborne gadget.  :=)

Why?  Don't assume the tank must be metal (though an aluminium can or
similar nosepiece comes to mind) or that it must be round.  A closed
cavity (bulkhead) anywhere in the model can be used.

Note: sensitive to solar heating.
--
Cheers,
Paul B.

>similar nosepiece comes to mind) or that it must be round.  A closed
>cavity (bulkhead) anywhere in the model can be used.
>
>  Note: sensitive to solar heating.

Note, in my application the internal temperature of the model is subject to
possibly intense temp variations with little if any correlation to outside
air temp.

Andy

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