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May 10, 2010
about 5 years ago
Scream if you have any issues with the handbook. I have had my share of headaches with o-rings and material selection etc. but I also have plenty of years of experience with it now. My little pet project involves a package for divers too. This sensor board will take care of at least two items that I want to be able to record etc. I have to design some sensors for the other items or pay through the nose to buy it off-the-shelf. I actually got the direction for this sensor from http://openrov.com Someone has a sensor using the main component, but with this .. it is one less board I got to bother making for now.
If you want to design your seal correctly, use the O-Ring Handbook that Parker puts out. These guys are the "Gods" when it comes to seals and seal design. I use their design guide all the time to get me in the ball park on pressure proof fittings. The directly link to their hand book is:
If nothing else, there is some excellent reading in this very comprehensive book.
That is correct .. I only bothered to state the measuring range. It doesn't matter how much overpressure the "sensor" can take, if you can't seal the rear from getting flooded out it is kinda of a moot point. If you are going to use it in seawater like I would want to, then you have to worry about how you are going to case it because of corrosion issues. At least they made the case out of stainless steel. It is easy to match with other metals or SS to reduce galvanic action. I might machine a fitting with an internal O-ring race to mate against the sensor wall ... the finish looks like it should be good enough for a soft seal.
According to the specification sheet it should be able to handle sea pressure or some other column of water down to around 426 feet.
Well considering that I make cables that are tested to 2000 PSI for external submarine pressure hull use ... you would be amazed at how fast water will find a way into something. It really revolves around what your depth is going to be. I am looking at 100+ meters.
As for pressure being transmitted through a potting compound, that all depends on the compound and how much pressure is actually going to be seen at the sensor. The material that you are sealing it with has to "give" in order for the pressure to be felt through it. If the material is not a pure fluid then it will resist pressure to some magnitude and once again, your pressure readings will be skewed. The bottom line is you can build it however you wish, I just know what has worked for me for the past 20+ years of dealing with enclosures at high pressure and more so in seawater ... which will do some nasty things to your materials.
I plan on getting one of these sensors and my game plan is to use PVC pipe or stainless steel tubing to go down to the sensor at board level and use epoxy to encapsulate around the sensor, inside the pipe etc. up to the point that you have the gel protected port that experiences the pressure. I will then seal my pipe with a cap and use a "pressure line" to go outside of the housing that the rest of my electronics are going to go in for my underwater probe package. I am debating on if to use a diaphragm at the end of my pressure line and have the entire tubing area filled with a fluid (such as oil) so I don't have to worry about burping the line each time it submerges. If you have air in the system, it will skew your pressure readings.
News - Sending a Balloon Into Ne…
about 9 years ago
Jonathan according to the online documentation for that module ... one of its operational limits is less 18,000 meters. Bottom line ... anything over 60,000 feet forget it.
That is why I gave the model number to a GPS module that does not have that Firmware restriction on it.
Other than some of the old Motorola OnCore modules .. it is the only one that I know that doesn't have a limit at 60,000 feet.
Since we launched our balloon on the East Coast area of Virginia and we had Hurricane Danielle kicking in the Atlantic Ocean, we were tracking speeds above 90,000 feet in the range of 300+ mph. They were realistic speeds because our balloon didn't come down until it was almost 120 miles away from our launch point. We had full radio transmission of GPS data during the entire flight.
Lesson Learned - READ the entire specification sheet on something you are buying. It clearly states all of the standard limitations for the module you got.
It is possible to get a GPS module that works greater than 60,000 FT. We sent our balloon up during the summer and reached a transmitted altitude of 103,258 Ft. We used the ISM300F2-C5-V0004 module from Inventek. This module is rated to 135,000 Ft. I also got the Active Patch antenna to help with reception of the GPS signals.
I wish this place would make the adapter boards to use with those modules and already have them SMD soldered. I did it myself but it was a pain in the rear. The module worked great and I think it would be a wonderful add to the inventory here.
Unlike what this guy did, since were were in the Hackerspaces in Space Contest, are budget was limited to $250 or less. I would have loved to used the wireless modems that was used in this project.
I had originally started the project with an Arduino board that I got from Sparkfun but ended up building a custom circuit because I needed the serial lines to the GPS and I didn't want to mess with SoftSerial; however, it was a good start since I never messed with one before.
If you want to see what we did, you can checkout our page at http://757labs.org/wiki/Projects/hackerspacesinspace
It was our first our first try at a balloon launch and we were very pleased with what we did.
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