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Topic: High Altitude Balloon: Testing array of temp/press/hum sensors @~-60C & 100000ft (Read 188 times) previous topic - next topic

RegisteredJack45

I'm researching my sensor options for taking external temperature, pressure, and humidity readings on my high altitude balloon project. We're going to ~100,000ft for ~3hrs flight time. I'd like to know if anyone has any good ideas as to which sensors would be a good pick, and which sensors I'm eyeing would be a bad pick. I want to take a few of each sensor that are commonly used and compare the results.

Since I'm looking to read external data, the sensor needs to be compatible with conditions as low as -60ºC. That's sort of the kicker and what makes some of the more commonly used sensors incompatible with the mission.

For IC based temp sensors I'm seeing most are incompatible with that low of a temp except the TMP102 which is good to -55ºC. It looks like a RTD or thermistor would fit most options at that low a temp, which requires as little as a voltage divider circuit to get an Arduino compatible input.

For pressure the sensor I'm liking most is the Honeywell ASDX series, good down to 10inH2O/2.5kPa and they have a tube for a hose to take external readings- the chip itself is only rated down to -20ºC but the hose attachment cures the problem. I'd like to compare to to the more commonly seen MPL3115A2 and even the BMP180 which has a pressure ceiling of about 9km (we're going to 30km) yet people still use them in HAB projects for some reason- I'd like to use one just to compare it's graph to sensors rated for the project.

For humidity, I'd like to see some advice because I'm having trouble finding something that'd work below -40ºC and viable as an external sensor. I'm looking at using the commonly used HIH-4030 alongside an HIH-4031 to compare data, theyre the same except the HIH4031 is hydrophobic coated and more compatible with moist environments yet SparkFun decided to put the HIH4030 on a breakout instead for whatever reason. I also want to use a DHT22 because it'd be an easy addition and this sensor is cheap and adorable.
I was able to find one humidity sensor on DigiKey (HPP804B130) but it's not on a breakout board and would require a custom circuit not necessarily outside the scope of our capability but outside of the time we're able to put into it.

Here's the list I've come up with

http://i.imgur.com/RdesxkK.png

As far as other hardware, I'm using an Arduino UNO R3, an Energizer LA522 Lithium 9V (it's good to -40ºC, 30g, and 1000mAh!), an Adafruit Ultimate GPS Board (which will give me altitude data to convert to theoretical pressure to compare with the actual pressure data), and I cant decide if I want the Logomatic V2 or the Adafruit Assembled Logging Shield.

Your sensor input (no pun intended) is appreciated.

Nick_Pyner

RTDs typically require an op-amp to get an adequate signal to Arduino.

http://openenergymonitor.org/emon/buildingblocks/rtd-temperature-sensing

el_supremo

The datasheet for the GPS unit used in the Adafruit device says that the maximum altitude is "18,000m (60,000 feet)" which is well below your expected altitude.
Isn't there an altitude limit placed on all GPS units - military restriction or something?

Pete

RegisteredJack45

I see that the spec sheet does state 18km quite clearly (in accordance with US regulation for import as I understand it?)
http://www.adafruit.com/datasheets/GlobalTop-FGPMMOPA6C-Datasheet-V0A-Preliminary.pdf

but the FAQ for their implemented product says it's good (but not guaranteed) for 40km and good for (but not guaranteed to work for) HAB flight
https://learn.adafruit.com/adafruit-ultimate-gps/faq

I suppose as long as they stay under the US mandated speed limit at that altitude they're in the clear? I dont know. Something about false flags for munitions on their tracking systems and such as I understand it.

You raised a flag in my head though. I should double check with my guidelines to see if it's allowed. I'm building this for NASA sanctioned project with my college so they're VERY by-the-book on rules.

"Can the Ultimate GPS be used for High Altitude? How can I know?
Modules shipped in 2013+ (and many in the later half of 2012) have firmware that has been tested by simulation at the GPS factory at 40km.

You can tell what firmware you have by sending the firmware query command $PMTK605*31 (you can use the echo demo to send custom sentences to your GPS)

If your module replies with AXN_2.10_3339_2012072601 5223 that means you have version #5223 which is the 40Km-supported firmware version. If the number is higher then 5223 then its even more recent, and should include the 40Km support as well

HOWEVER these modules are not specifically designed for high-altitude balloon use. People have used them successfully but since we (at Adafruit) have not personally tested them for hi-alt use, we do not in any way guarantee they are suitable for high altitude use.
Please do not ask us to 'prove' that they are good for high altitude use, we do not have any way to do so
If you want to measure high altitude with a GPS, please find a module that can promise/guarantee high altitude functionality"


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