# Altitude - barometer

Hi all,

I would like to measure altitude while sending an atmospheric balloon. The altitude I would like to reach is above 30km (100'000 foot for my US friends :) ).

I saw couple of sensors (BMPxxx, MPLxxx), but I wonder if I'm reading their datasheets correctly, as none of them look to be reaching 30mBar, and if my calculations are rights, I think this is what should be the pressure around 30km.

Does one of you have any suggestion? If you are thinking about an alternative way to measure the altitude, feel free to suggest of course !

Thanks all, Ludo

Those sensors are indeed only to be used on earth. The 30 km is the Stratosphere. I think the pressure is 10mbar at 30 km. Should the sensor be able to withstand -50 degrees Celsius ? Or is is protected against the temperature ?

The sensor will be somehow protected against low temp, we will be in storing it in a box with large border, and we will try to limit the air exchange (even if we still need some for pressure balance :) ). We also plan to heat the box internally. Not sure how much we will be able to balance with the -55 degrees C from outside, but we try to keep the box as warm as possible.

At an altitude of 30km, I'm unsure what would be the pressure exactly, but from what I read, it was about 10mbar as well. We pulled data from a site and draw a graph about it: https://docs.google.com/spreadsheets/d/1vN6A6cp5ad9ABYSzyYsBeURFJsVaMY-GcVkaKvdFCo8/edit?usp=sharing

We checked already some other sites, and especially some other articles about people sharing their experience around weather balloon, but we also try to learn from our own investigations about each point, and not just mimic an already existing experience. :) We also are limiting the budget for each electronic piece. We know there are solutions which are more expensive (around \$100 or more), but we wanted to know if there was any other cheaper solution already existing.

As far as I know, you need a special sensor. Perhaps it is hard to make an absolute/baromic pressure sensor that also measures around 1kPa.

You can search at Mouser. http://eu.mouser.com/Sensors/Pressure-Sensors/_/N-6g7qc Select a absolute pressure sensor that starts at 0kPa and sort for the lowest price. That way I found a HoneyWell SSC Series TruStability sensor of 37 euros.

Because the BMP180 is so cheap and very accurate, I would like to use it myself for other things. Also others ask questions on this forum for a allround absolute pressure sensor. But so far, I have not found something like the BMP180 that has a larger range.

Thanks for the link, really helpful. It looks like for a decent amount of money, we could get what we want: measure the altitude thank to the pressure.

I'll look at the sensor you suggested. They look to have an office in France, I'll call them tomorrow.