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Digital read out of air pressure over time

  1. Jan 11, 2008 #1
    I am trying to get some information to see if there exists a sub-system which can monitor air pressure (~200 psi) over a certain amount of time (less than 5 min.) and can output the readings so the information can be input real time or saved to a file which can later be input to Excel.

    Anybody having any information would be helpful (background info, experience, web links, etc.)

    Thanks,
    -pud-
     
  2. jcsd
  3. Jan 11, 2008 #2

    FredGarvin

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  4. Jan 11, 2008 #3
    Thank you...

    This is definitely what I was looking for. I really appreciate those links. I'll will have more questions soon.

    Thanks again
     
  5. Jan 11, 2008 #4

    mgb_phys

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  6. Jan 11, 2008 #5
    my upcomming test....

    OK, here is what I'm planning on doing...

    I have some cylinders...OK, a butt load of cylinders which need to be pressure tested to about 225 psi each for under 5 minutes each. The plan is to develop a manifold that each cylinder is attached to. The manifold will provide the air supply. I'll have a pressure reading at each canister...thinking I might be able to test 5 or more at a time. The air supply (no not the group; hee hee) is going to be removed once the pressure is added to the cylinder. The test takes place as a visual under water...obviously looking for bubbles... I want to be a little more scientific about it and have the pressure readings captured, hence the data logger, and recorded every second with some accuracy. That way, in the event the operator doesn't see any bubbles, they can see a pressure drop at some point. Being that the air source is removed, any change or drop in pressure should be seen.

    With the data logger, is there a way that i can be recording 5 or more different pressure readings? If so great. If not, any suggestions?

    Also, any suggestions on a compressor that will get up to 225 psi? Is the more economical choice using a basic compressor, then "re-compressing" the air as in those air booster things?

    Any help suggestions or ideas are always welcome.

    Thanks
    pud
     
  7. Jan 11, 2008 #6

    mgb_phys

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    How big are the cylinders? this will effect the size of the air compressor you need.
    If they are failry small then either a scuba tank or an air brush compressor will be fine.
    Depending on how large the cylinders are the pressure test might be a lot less accurate than the bubble test.
    Imaging something the size of a scuba cylinder, these contain 80 litres of air at atmospheric pressure so the change in internal pressure from them losing a small 0.1cc air bubble would be an almost undetectable change in pressure. For a smaller cylinder the pressure change is easier to detect.
    To test 5 at a timeyou would need 5 valves to separately seal each cylinder and you would need 5 sensors and a 5 channel logger.
     
  8. Jan 11, 2008 #7

    russ_watters

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    These guys rule: http://www.onsetcomp.com/

    I've never used one of their pressure gages, but they have 4 channel loggers for about $115 and gage or dp sensors for $190 each. You're unlikely to find anything that can compete with that. The 4-channel logger with 4 temperature probes is what I used here: https://www.physicsforums.com/showthread.php?t=205920&page=2

    That Pico logger looks similar to the HOBO, but it looks like it has no memory - works only with a PC. But it has 11 channels as opposed to the HOBO's 4. And it's $185, which is pretty good. For the sampling rate, is 20 "kS/s" 20,000 samples/sec? I'm actually thinking of an application where I could use something like that at home...
     
    Last edited: Jan 11, 2008
  9. Jan 14, 2008 #8
    Thanks for all of the responses...

    The volume of the cylinder is ~ 1 cubic inch. The visual check is definitely going to happen, but I want to log all of this automatically as well.

    Omega seems to have some neat stuff as well.
    http://www.omega.com/ppt/pptsc.asp?ref=OM-CP-PRTEMP1000&Nav=dase01

    It seems like they have a specific data logger for just for pressure applications, up to 500 psi within 0.05 psia. That should be plenty accurate for this test. EXPENSIVE though, so the previous thread's suggestion may make more sense.

    Another question that I wanted to post, was what are everyone's thoughts on a compressor or "system" that will allow me to safely reach the 200 (+25) psi range that I am going to need for the test? Other than what a basic Goggle search has turned up, I'm not sure what else is out there.

    Again, I appreciate everyone's help and input.

    Thanks,
    pud
     
  10. Jan 14, 2008 #9

    FredGarvin

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    With such a small volume for the cylinders, one thing you may want to look at in stead of a compressor is using compressed air cylinders. A large K type bottle with 2200 psi source pressure would handle quite a few of your bottles before you needed to swap it out for a new one. It would be pretty inexpensive and quiet. The only thing you would need is a precision regulator to knock down the pressure to your test point and a way to slow down the time to pressurize your bottles, i.e. an orifice. It's an option to consider.
     
  11. Jan 14, 2008 #10
    Definitely going to be considered. Somone outside of the "forums" environment suggested something similar to that as well.

    Oops, just noticed that I said I did a Goggle search when it was actually a Google search....
     
    Last edited: Jan 14, 2008
  12. Jan 18, 2008 #11
    It looks like the large tank for a supply, then regulated down to a usable pressure is the way to go. Will any inert gas work? Can you rent cylinders of plain old air? I'll try and post a picture of the apparatus when constructed.
     
  13. Jan 18, 2008 #12

    FredGarvin

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    You can rent compressed air. They will usually break it down into breathable air and industrial air (which may have a slight oil or other contaminant amount). I guess as long as you are looking at just the pressure, anything that creates that pressure is going to be OK. I don't think you'll beat the price of compressed air though.
     
  14. Jan 18, 2008 #13

    stewartcs

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    Based on your setup you should not need an inert gas. The only caveat with using compressed air (a non-inert gas) is if you have a high pressure that comes into contact with a hydrocarbon (i.e. grease). Shouldn't be an issue for you, just something to keep in mind in case you ever run across it.

    CS
     
  15. Jan 18, 2008 #14
    Well, there is always a chance that these could come into contact with a small amount / residue of oil since we are machining the canisters. Will compressed air still be OK?
     
  16. Jan 18, 2008 #15

    mgb_phys

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    Yes, just don't use compressed oxygen!
    Normal compressed air usually has some oil contamination anyway ( you pay a lot more for clean oil-free breathable air ).
     
  17. Jan 18, 2008 #16
    Can't seem to recall the set of equations used to figure how how long I can use a supply at a certain volume and pressure to fill a certain volume and pressure.

    Any suggestions
    ~2000psi in ~80ft^3 filling a can to ~200psi in ~1in^3
     
  18. Jan 18, 2008 #17

    mgb_phys

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    Just put everything in the same units then remember that at a fixed temperature, pressure * volume is constant.

    Remember though when a cylinder is quoted as 80cu ft (eg standard Al scuba diving cylinder) that is the amount of air at atmospheric pressure that was put into it. It is not 80cu ft * 2000psi!

    So 80 cu ft = 140,000 in^3 * 15psi, Fills a can of 1 in^3 at 200 psi
    (140,000 * 15) / (1 * 200) = 10,000 times
     
  19. Jan 18, 2008 #18

    russ_watters

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    Google gives much better search results in most cases...
     
  20. Jan 21, 2008 #19
    This is pretty much what my dad and I came up with over the weekend. It matches, so typically that's a good thing.

    good point about the atmospheric temperature thing though... thanks.

    Yes, Google searches work better than Goggle searches...

    I'll do my best to post whatever I end up coming up with for this thing. One thing that I did want to share with the "community" is that if you need to make a manifold for something carrying air, any other gas (most likely) or liquid, maybe, a good way is to take a chunk of aluminum and start drilling some holes. To start with the manifold for this project, I drilled a hole straight through, long ways, then drilled perpendicular holes which then entered the other hole. This allows me to plug in the air source, plug in a pressure guage, plug in a bleeder valve, etc. I can then have a bunch of outputs for the air, gas, or liquid to flow. By plug in I mean, tap the hole, then thread the thing in....or put a gasket around the hole, then clamp your part to it.

    Well that's my cranial dump for the moment. Like I said, I'll try to post more when I can.

    -pud-:biggrin:
     
  21. Jan 22, 2008 #20

    FredGarvin

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    Or you can save your time and simply purchase one to meet your needs. I routinely buy manifolds already manufactured in a number of configurations. A nice one that is large will run about $80. You can also buy square ones through McMaster-Carr.

    http://www.dfburnham.com/pages2/manifold.shtml
     
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