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Is this an air-pressure sensor?

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VulcanBB18

Tue Oct 20 2009, 08:59AM

Registered Member #2376 Joined: Mon Sept 21 2009, 05:13AM
Location: Brisbane, Australia
Posts: 14

Hi All,

I am working on a weather station project (using a free datalogger I got from a server-room throw-out) and I have a board that someone gave me years ago that has an unusual looking sensor on the bottom. I think at the time it was mentioned that it came from a weather balloon, but that could be incorrect or my memory being fuzzy.

The sensor in question looks like a sealed chamber or a pair of sealed chambers, I thought maybe for measuring air-pressure or maybe some other atmospheric reading?

I've attached some images of the sensor in question and the top-side of the board. The sensor I'm wondering about is the round looking metal thing with a white supporting square (ceramic by the looks). The chips on top are a set of gates, an analogue multiplexer, a counter and a timer. Any clues would be greatly appreciated!

cheers

Jacob

Proud Mary

Tue Oct 20 2009, 09:42AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi there Jacob,

it is indeed a Radiosonde. You can tell because of the two silver plated UHF inductors, which look right for the 400-406MHz weather balloon band.

I'd guess the sensor to be a capacitive steel aneroid.

I reckon the line of inductors with the crystal at one end and the UHF coils at the other will be the Local Oscillator, Frequency Multiplier Chain. The frequency of the crystal is usually written on the side of the can, from which (since you know the final output frequency to be about 403MHz) you can deduce whether the multiplier be a doubler or a tripler. Typical RF output of Radiosondes is 300mW.

This one looks fairly antique because it doesn't have Loran-C or GPS.

Conundrum

Tue Oct 20 2009, 05:43PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

interesting..
i have one here with a similar sensor, was planning to use it as part of my weather balloon project.

they change capacitance with altitude, so a suitable VFO connected to a PIC will work.

the slight annoyance is that this change is negligible (fractions of a pF, comparable with a tuning diode) so another circuit might be a Wheatstone bridge using a tuning diode as the opposing side.

regards, -A

Herr Zapp

Tue Oct 20 2009, 06:15PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Vulcan -

You can see a datasheet on on one of Air, Inc's current radiosonde models at: alma.nrao.edu/development/site/.../radiosonde/ IS5A2.pdf

They still use a variable-capacitance aneroid sensor.

Regards,
Herr Zapp

Proud Mary

Tue Oct 20 2009, 07:29PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I heard on the radio of an absolutely amazing and extremely simple use of a weather balloon together with camera cell phone technology. Being a radio programme, there was no great technical detail, but in essence the camera cell phone was launched beneath the balloon, and so produced a continuous video stream looking earthward until the balloon exploded at about 50,000 feet. It was said that the entire curvature of the earth could be seen!

I have sourced weather balloons for Â£15 (about $25) and hydrogen from British Oxygen, but I don't know much about camera cell phone technology, but I bet someone else here does!

klugesmith

Tue Oct 20 2009, 07:56PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Unfortunately lost in the heap, I have an even more primitive radiosonde box, complete with a vintage battery.

camera cell phone was launched beneath the balloon, and so produced a continuous video stream looking earthward until the balloon exploded at about 50,000 feet. It was said that the entire curvature of the earth could be seen!

Check out these high-altitude aeronautical adventures from the same institution that brought coin-shrinking to Maker Faire:

There are some interesting comments about GPS altitude and speed limits.

VulcanBB18

Wed Oct 21 2009, 12:46AM

Registered Member #2376 Joined: Mon Sept 21 2009, 05:13AM
Location: Brisbane, Australia
Posts: 14

Thanks for all the responses, certainly made finding information about the device easier once I got some leads from here :)

Okay for my purposes there may be easier ways to achieve a barometric reading. Interesting to note there is a VFO on the board as mentioned by Conundrum so I guess it uses that method.

Don't really want to junk any of the board now that I know for certain it is a radiosonde!

Proud Mary

Wed Oct 21 2009, 02:50AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

VulcanBB18 wrote ...

Okay for my purposes there may be easier ways to achieve a barometric reading. I

I have some resistive barometric sensors which work on the Wheatstone Bridge principle. I'll send you one if you'd like to contribute three dollars to 4HV. They can detect a change in altitude of a couple of feet.

VulcanBB18

Wed Oct 21 2009, 04:27AM

Registered Member #2376 Joined: Mon Sept 21 2009, 05:13AM
Location: Brisbane, Australia
Posts: 14

That's a deal Harry! :)

Proud Mary

Wed Oct 21 2009, 04:40AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

VulcanBB18 wrote ...

That's a deal Harry! :)

If you'd like to send me your address in a PM, I'll post the sensor to you when I go to the Post Office on Thursday

When you send your contribution to Chris Russell, can you make sure he understands it is in fact from me - Harry

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