Test Chamber

[splatula]

I'd like to see a Alti build a smaller portable test chamber similar to FXC's P/N 711-07146. Is there any plan for this? Of course I'm looking for a unit that can be better priced that FXC's.


Cheers,
Abbie
Splatula Rigging, LLC
www.splatula.com

[Roger Allen]

I'd like to see a Alti build a smaller portable test chamber similar to FXC's P/N 711-07146. Is there any plan for this? Of course I'm looking for a unit that can be better priced that FXC's.


We have been looking at developing a replacement for the old SSE Utility Test Chamber.

What internal dimensions would work for you?

[splatula]

I will come up with exact numbers but it can be fairly small. The idea is to be able to test single items such as an FXC model 12000, a modern AAD such as Argus, an altimeter such as the Altimaster II, etc.

cheers,
Abbie

[SkyZot]

Is there progression on the testchamber ?
I am intrested too in such a small testchamber....

[Roger Allen]

Is there progression on the testchamber ?
I am intrested too in such a small testchamber....

Let me know the internal dimensions that you need.

Roger

[kabatronix]

this is my very basic proof of concept homebrew low pressure chamber:http://www.kabatronix.de/afs/dscf0044.jpg


any small vacuumpump will do (mine is from medical surplus, ebay :-), look for a plastic can with rubber seal in your local department store, glue in a rubbertube, attach a pressure gauge capable of -1bar, here we go.

next chamber will be made from acrylic glas, vacuum pump will be timecontrolled to simulate climb and shutdown at selected level automaticly.

controlled increase of pressure by means of two ventiles: first fast path to simulate freefall, second slow pass to simulate canopyride, both time and pressure controlled.

i will use nothing new, only ebay junk and trash lying around in my workshop, no expensive stuff ;-)

by the way, for those interested: mmWS means milimeter water column
1 mmWS = 9,80665 Pa (http://de.wikipedia.org/wiki/Pascal_%28Einheit%29)
10 mmWS = 1 p (http://de.wikipedia.org/wiki/Pond)/c (http://de.wikipedia.org/wiki/Zenti)m (http://de.wikipedia.org/wiki/Meter)2 = 98,0665 Pa (http://de.wikipedia.org/wiki/Pascal_%28Einheit%29)
1 mWS = 7453054/101325 mmHg (http://de.wikipedia.org/wiki/MmHg) ≈ 73,556 mmHg (http://de.wikipedia.org/wiki/MmHg) = 73,556 Torr (http://de.wikipedia.org/wiki/Torr) ≈ 0,09678 atm (http://de.wikipedia.org/wiki/Physikalische_Atmosph%C3%A4re)
1 mWS = 9,80665 k (http://de.wikipedia.org/wiki/Kilo)Pa (http://de.wikipedia.org/wiki/Pascal_%28Einheit%29) = 98,0665 h (http://de.wikipedia.org/wiki/Hekto)Pa (http://de.wikipedia.org/wiki/Pascal_%28Einheit%29) = 98,0665 m (http://de.wikipedia.org/wiki/Milli)bar (http://de.wikipedia.org/wiki/Bar_%28Einheit%29) = 0,0980665 bar (http://de.wikipedia.org/wiki/Bar_%28Einheit%29)CU

kaba

update:

this one is capable of 5500 m maximum altitude, climbspeed 1 minute, there´s a hold now for about 30 minutes at 5300 with pump detached and rubber tube sharply bend to seal the chamber.

there are very fine small stress crackles on the inside of the lid.
i´ll keep you informed, this can was a real cheapo one, you should be better off with one of higher quality ;-)

lucky implosions to all of you...

[kabatronix]

ok, another post, same issue:
"atmolette" secrete suction pump has been changed to excenter driven two-stage membrane pump, which is capable of at least 100mbar low pressure.
i had to stop the pump running when my cheapo chamber started to make crackling noises then ....

(just to remind you: that´s really far out, 264 mbar is 30.000 feet ;-) )

a mechanical precision low pressure gauge, a barometric ventile to set maximum altitude (safety!!! :bump:) and an adjustable pressure outlet have been added to help simulate a skydive manualy.

this setup was already used to test and align a broken altimeter after repair, my neptune was used as reference :-)

i shopped another membrane pump on ebay tonight, new low pressure chamber will be finished within a fortnight.
the digital vacuum controllers will arrive this week. they will allow to automate the test cycle and to drive a digital altitude display.
i also think about a sensor controlled peltier element to simulate icy or hot conditions when testing altimeters.

i will post some more pics of my experiments later.

feel free to ask questions how to build your own test chamber.
if you already built one please share your experiences, thank you :-)

keep it save,

as soon as i finish the massive acrylic glas test chamber, i will try to destroy the cheapo one by pure atmosphere.

i will post the results.... :-)

http://www.kabatronix.de/afs/dscf0050.jpg
"new" stand for fast setup of testequipment, on top right the dc-driven two-stage vacuum pump,
left side a barometric pressure valve to adjust minimum pressure, in front "old school" pressure gauge,
down on the right the now confirmed 100mbar proof (it simply did not collapse so far ) low pressure chamber ;-)

http://www.kabatronix.de/afs/dscf0058.jpg

here we go a bit more professional:
right side of stand: ac mains driven laboratory vacuum pump with fastlock pressure tube plug,
and good old test chamber (had no time yet to glue the new one together),
in the middle mechanical pressure gauge, on top of it digital pressure gauge supplying analog dc output and barometric valve.
left side of stand: dc-powersuply, programmable transmitter and digital display of metric altitude.

the programmable transmitter is used to transform exponential pressure related analog output of digital pressure gauge to linear dc-voltage to drive digital display to show correct altitude.

here is were i need some help from alti-2 professionals:
what is the reference atmosphere model when you do adjust alti-2 altimeters?
neither neptune nor any other altimeter seem to show altitude accuratly given a fixed pressure.
sophisticated temperature compensation even in mechanical devices?

give me a hint please ;-)

kabatronix

[kabatronix]

i do not know if anybody cares, but as you can see the testchamber project grows and grows.
most equipment is surplus stuff out of industrial production sites bought at ebay or taken from to be torn down factories when looking for cool base exit points ;-)

there is no need to spend a fortune for a test chamber as you can see, just use your brains and your fantasy ;-)

cu

kaba

[MrBrant]

Hey Kabatronix - nice work on the chamber!!

I'm very interested to see how this project turns out (you've got me wanting to build my own too dammit! ;) )

As for the atmospheric pressure reference model you speak of - I think you'll find it a bit difficult to find one that fits this application.

About a year ago I built a digital altimeter for a school project. (I still use it today - it was a very useful endeavor!) Roger and the guys at Alti-2 helped me out a lot as I was doing this project. (I didn't really want to use a home-built an experimental test chamber, to design an experimental altimeter in the 3 months that I had to complete it).

The chamber I was able to use had a simple aircraft altimeter on it. (this, of course, matched up almost perfectly to the skydiving altimeters). To simulate descent rate, I use the most accurate method ever - counting :rolleyes: . (roughly 5.5 seconds per dial revolution [1000 ft]. Worked out surprisingly well!)

What I found was the models I had weren't worth the bits they took up on the internet. It started out pretty accurate at low altitudes, but would taper off a lot as you got higher. I would have been much better off logging readings, and creating my own transfer function - rather than trying to "fix" the one I had.

So, I guess what I'm saying is - don't' be surprised if you can't find one. (If you do - send it my way!!). I would suggest trying to pick up an aircraft altimeter - might be more accurate and have better resolution than a skydiving altimeter.

Have fun! :D

(Pics attached. Ignore the blasphemy in the chamber pic - it was before I bought my Neptune!!!)

[tigredrako]

What kind of algoritm or formula are you using to transform the output from the pressure gauge to the digital display of metric altitude?, this calculator http://www.digitaldutch.com/atmoscalc/ may help you determine how accurate is the translation from pressure to altitude.

[kabatronix]

hi tigredrako (http://forum.altimaster.com/member.php?u=299),
in the above setup linear voltage output of the pressure gauge is send to an universal programmable transmitter. i have programmed 10 values according to standard atmosphere and temperature decrease to achieve sufficient accuracy between 0 and 5000 m. output is then 0mA for 0m and 20mA for 5000m altitude.

while doing my test runs there is actually NO temperature decrease!!!

so i think i have to change the values in the final setup.
as long as noone of the alti-2 tech guys sends me their test table for 20°C roomtemperature testing over the whole altitude range i will use my neptune as a reference.

but i havew no information, in how far mechanical altimeters are temperature compensated.

probably they do always read out the standard atmosphere altitude at a given pressure even if temperature is totally different in real life.

by the way:
my new big acrylic glas chamber is so far finished, holds low pressure for several hours with a loss of perhaps 10mbar, i had no time yet to analyze that accurately.

there will be a special pressure sensor for accurate altitude readout solely and the digital gauge will be used only to switch the vents to simulate a standard skydive.

i hope to implement all the fittings and pressure gauges at christmas time for i havn´t finished the neptune translation yet.

i´ll post some pics the next days :-)

cu

kaba

[kabatronix]

this is the all new acrylic gls testchamber, which i finished in december 2007 and was used to analyse, cross-check and align lots of faulty, condition-unknown and repaired altimeters since then.

automated skydive simulation has not yet been implemented, but will probably be finished next winter ;)

it´s a very cheap and simple construction, therefore very stable and effective. it keeps low pressure for quite a long time without esoteric seals, just a latex o-ring glued to the base and self-adhesive foil as opposite elastic material under the top cover. the acrylic glas blocks have been glued together with a special glue used to build aquariums, also the tubes and valves are from a pet shop. all the fittings and screws are from home depot.

aligning the blocks after glueing is a bit tricky, i used a belt grinding maschine for the raw job and a polishing disk for the finish.

http://www.kabatronix.de/afs/%20bild%20003a.jpghttp://www.kabatronix.de/afs/bild%20007a.jpg

rubber feet are still missing, also a second access point for additional sensors and vent valves.

cu all on 8th of august @ WOM2008 (Wings Over Marl) :bump:
www.fallschirmsport-marl.de

kaba

[patrick076]

really very nice post i am new my first post here