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  1. #1
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    16th February 2017
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    Altimeter testing rig ideas?

    Looking for ideas/parts/sources for said parts to build a reliable/repeatable setup to test my electronics. So far I have a handheld vacuum pump w/gauge, a stand alone vacuum gauge and a foodsaver. Am looking a picking up a 1 gallon widemouth canning jar and attachment for the foodsaver. Any ideas on a bleeder valve type setup to regulate vacuum? How about inches of mercury to altitude comparison #s? All I've managed so far is to make leds light up in a cobbled together rig, it allows me to see that things work but no real data. I'd like to be able to test as flown setups complete with e matches.


  2. #2
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    23rd July 2011
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    Altimeter testing rig ideas?

    Quote Originally Posted by Wallace View Post
    Looking for ideas/parts/sources for said parts to build a reliable/repeatable setup to test my electronics. So far I have a handheld vacuum pump w/gauge, a stand alone vacuum gauge and a foodsaver. Am looking a picking up a 1 gallon widemouth canning jar and attachment for the foodsaver. Any ideas on a bleeder valve type setup to regulate vacuum? How about inches of mercury to altitude comparison #s? All I've managed so far is to make leds light up in a cobbled together rig, it allows me to see that things work but no real data. I'd like to be able to test as flown setups complete with e matches.
    If you already have an iPhone 6 or later it has the ability to show you pressure and corresponding altitude using an app called My Altitude:

    Click image for larger version. 

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    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  3. #3
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    Very cool. Hopefully there's an Android version? Thanks Steve.

  4. #4
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    11th February 2018
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    The usual way to do this is with a shop vac. Tape shop vac over the pressure equalization hole in your av bay and fire it up to draw a vacuum. Turn it off to land. The pressure is released fairly gradually. You could get fancier with a relief valve, but I’ve found this to be sufficient. I also design my altimeters with a “test cycle” that will run the software with canned values to simulate a real flight. This lets you make sure everything is working at the field too.

    For the little bmp 280 type barometers, you can just “suck” on them to draw slight vacuum to make sure they’re working too. My record is 900m.

    The relationship between pressure and altitude is a fixed function - and all the libraries I’ve used will do the conversion for you given today’s pressure at sea level. “Relative” altitude is really what you need. I see as much as 100m difference for the “pad altitude” depending on the weather, but the relative altitude isn’t impacted by enough to program in the pressure at sea level for every flight.

    Real world testing is important. Fly your altimeters and log the data to make sure they work before using them for any dual deployment. In my case, I generally trust my engineering and static testing. My soldering - not so much.








    Sent from my iPhone using Rocketry Forum

  5. #5
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    I've done the shop vac thing and while it does tend to show weather or not something works, I'm more interested in accuracy/repeatability. I'm sure I can find current density altitudes online and with the app Mr. Shannon mentioned be able to get "good" data. Not currently planning anything specific, mostly out of curiosity since I've seen some "abnormalities" in flight recordings. Basically eliminating the wind variable should give me better accuracy?

  6. #6
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    If you are that worried about repeatability, put in 2 altimeters & be done with it. Most altimeters that fail are due to user error!
    Tim
    L3 NAR 98225

  7. #7
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    6th September 2009
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    Are you building your own or using a commercial altimeter? If commercial, then I agree with timbucktoo - the problem is usually the user, so what's the point? The programmer of the device may cause some variation in data filtering or deployment logic, but the barometer itself is pretty robust. They all do a pretty good job of measuring the air pressure they are exposed to. Why do you think an iPhone app is any more "accurate?" All barometers convert to altitude using the same Standard Atmosphere model which assume standard day sea level conditions - something that rarely occurs in real life. As mentioned above, the altimeter can vary by 100m at the pad just with local weather.

    Not sure what you mean by "wind variable."

  8. #8
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    If your tubing is the right size, get a vacuum T-fitting at an auto parts store, then add a small valve (like would be used on a fish tank)

    I usually do mine inside a re-purposed pickle jar with a hole in the lid. I have a manual vacuum pump from the zip-lock vacuum bag system. As long as I pump faster than it leaks, I'm good...
    Terry

    NAR L1
    L2 is on hold, maybe never

  9. #9
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    13th October 2014
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    My rig is a Foodsaver Marinating Bowl, eventually I will get around to adding a gauge and exterior wire terminals to it for ematch and igniter tests, but for now it tells me that the altimeter works and if two are tested at the same time how close they read to each other, for indicators I use incandescent Christmas tree light bulbs.
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  10. #10
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    I guess I should have know better...

  11. #11
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    29th December 2013
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    I use a hand pump and Xmas tree lights.
    https://www.harborfreight.com/automo...kit-63391.html

    Sent from my LG-V521 using Rocketry Forum mobile app
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  12. #12
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    23rd July 2011
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    Quote Originally Posted by Wallace View Post
    Very cool. Hopefully there's an Android version? Thanks Steve.
    I’d be very surprised if something similar weren’t available.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  13. #13
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    Quote Originally Posted by Wallace View Post
    I've done the shop vac thing and while it does tend to show weather or not something works, I'm more interested in accuracy/repeatability. I'm sure I can find current density altitudes online and with the app Mr. Shannon mentioned be able to get "good" data. Not currently planning anything specific, mostly out of curiosity since I've seen some "abnormalities" in flight recordings. Basically eliminating the wind variable should give me better accuracy?
    Mr.?

    I’m just Steve. Any respectability is long gone.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  14. #14
    Join Date
    31st December 2011
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    Here's one that I built 5 or 6 years ago. I still use it.

    http://www.rocketryforum.com/showthr...imeter-testing

  15. #15
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    6th September 2009
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    If you want to play with data, then consider a Raven. It is the most thorough that I have used. It will export the pressure measurements AND the altitude, so you can check how the Standard Atmosphere model was applied. I did this and confirmed that indeed the standard day model (with no corrections) is used. Check the Raven User Guide for a discussion on how baro altitudes are in error up to 10% without temperature correction. The NAR was addressing this issue for altitude records/competitions a few years ago.

    The atmosphere models used by the simulators (RS, OR, RAII) can be called more "accurate" than most electronics, since they correct for local pressure, temperature, and even humidity.

  16. #16
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    25th July 2012
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    I built my own using the same gallon glass pickle jar method. I built mine specifically to test various manufacturers altimeters at the same time in the chamber. I used 12v light bulbs for ejection charge simulators. Videotaped the whole mess (so long ago it was VHS) so that I could slow down the playback and actually see what happened in sequence.

    I also used a small commercial vacuum from a used medical supply shop. Worked almost too well. First simulation said it was 80K in altitude. If I was going to build another one, I'd get one with an adjustable vacuum level instead of the "all-on" or "all-off" unit that I had.

    Lastly, whoever said to use a fish tank "relief" valve is right on. Just make sure you use a brass one and not one of the plastic ones. I soldered a brass one to the lid of the pickle jar. Makes for easy and slow vacuum release. Eventually I learned to close it slowly after I turned on the pump. This allowed for a "slower" vertical flight.

    Lastly, don't be surprised at variations in altitude readouts even from the same manufacturer. I'd get 8% to 12% differences from the same manufacturer with different versions of altimeters in the flight simulation chamber at the same time.

    Either way, I had lots of fun with it.

    Enjoy!

    Brad, the "Rocket Rev.," Wilson


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