Searching for an air pressure sensor...

Discussion in 'Electronics Resources' started by Sparky49, Aug 14, 2011.

  1. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Hi everyone.

    I've been searching for weeks now...Trying to find an absolute air pressure sensor which will measure up to 5 PSI.

    Why is every darn 5 PSI sensor differential or gauge?

    I'm begging you guys, does someone know of an absolute 5 PSI air pressure sensor?

    Perhaps, if someone is willing, we could chat over PMs, as I'm getting worried that I'm being seen to 'clog' up your forums with my constant questions...:(

    Thank you very much for your time guys, I'm feeling a bit down at the moment...

    Sparky
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
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    google "precision pressure transducer"
     
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  3. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Sorry if I'm being dumb, but all the results which come up for me are for differential pressure.:confused:
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    How about one of these? http://parts.digikey.com/1/parts-kws/absolute-pressure-sensor

    As far as "clogging up the forum." Thats what it's for. What doesn't help you may be of help to the next person, or even those who answer.

    You may have to use a sensor rated for higher than 5psi. They will read up to their limit. A car MAP sensor may even work for you?
     
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  5. someonesdad

    Senior Member

    Jul 7, 2009
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    Any differential pressure sensor can be turned into an absolute sensor -- just pull a vacuum on one of the inputs.
     
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  6. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    How would I pull a vacuum and maintain it? Suck?:rolleyes:

    The problem I have is that I'm using a transceiver module which has to have a digital input. As such I'm going to need a ADC.

    One 5PSI sensor I looked at today measured it in 7.5mV/PSI. When my sensor is in general use, it will only be measuring between 0.5-2 PSI. If I'm wanting 0.01 PSI intervals, the ADC would have to convert something like 0.075 mV intervals, which is really quite small...

    So would the problem be magnified if I had to use a higher PSI sensor?
    ________________________________________________________________
    I like the idea of creating a vacuum. How would I go about doing that?
     
  7. someonesdad

    Senior Member

    Jul 7, 2009
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    Exactly. But there are lots of ways to suck besides being a politician.

    For general work around the home and shop, I use a Mityvac. They aren't very good vacuum pumps, as they only get down to on the order of 85 kPa (640 torr). An industrial roughing pump will get down in the 10 to 100 mtorr range (760 torr = 1 atmosphere; the torr is one of the more commonly-used pressure units in the vacuum world) and of course, you need to go to more sophisticated pumps for lower pressures, but these will undoubtedly be out of the range of your needs and pocketbook.

    I believe some HVAC techs have turned old refrigerator compressors into somewhat capable vacuum pumps. You might search the web for more info. You can also find surplus pumps (Gast, GE, etc.) from the surplus companies.

    You don't say what your application, experience, or budget are, so it's hard to be more specific.

    One technique to keeping the vacuum is to pump out a copper tube, then crush the tube to provide a seal. A subsequent dip in a sealant like epoxy wouldn't hurt either.
     
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  8. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    The pressure sensor will be used to measure the pressure inside my bagpipes...

    As for my experience, I wouldn't say I was experienced at electronics, but I wouldn't call myself a novice either.

    I'm kinda hoping to market the sensor if it works, and is reliable, so I really wanting to keep costs down as low as possible.
     
  9. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    I tell you what, when I get 100 posts I'll post a video of me playing, so you guys can enjoy the wonderful sounds of the bagpipes...





    :D
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Are you sure you want a absolute pressure sensor? A vapor pressure sensor might work better, it's for lower pressures. I know this is a link to car sensors, but explains a lot about the different type sensors and even gives some circuits on how to use them. Hope it helps.

    http://www.autoshop101.com/forms/h35.pdf
     
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  11. #12

    Expert

    Nov 30, 2010
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    I was on post #8 when I realized your terms are confusing. When you say, "absolute" pressure, that means p.s.i.a. to me, "pounds per square inch compared to absolute vacuum". I don't believe your bagpipe operates at .5 to 2 psia. I would believe it operates at .5 to 2 psig which means pounds per square inch, gauge, which means psi above atmospheric pressure.

    Second idea: If your transducer outputs microvolts, you can amplify the signal with a DC coupled opamp before putting it through an ADC.

    Third idea: When an HVAC person seals a vacuum, he pinches the tube (as someonesdad said) and then brazes it shut with 5% silver solder. That will hold for about 100 years. An HVAC vacuum pump goes down to about "50 microns". If I remember correctly, that's 50 millionths of a psi. Close enough for bagpipe work.

    and that's about as much as I can contribute.
     
    Last edited: Sep 8, 2011
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  12. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    SO just to clarify, the pressure in the pipes would be ~17 PSIG?

    So the pressure would be akin to a on the graph (atmospheric b), and not c?

    Thanks.
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    No the pressure in the bagpipes would be ~15.2-16.7 PSIA; and at the same time it would be ~.5-2 PSIG. pressure (when you're dealing with terms like PSIA, PSIG, PSID, etc) is sorta like voltage. it is only measured as the differential between one point and another point. the most common is PSIG, meaning the difference in pressure between the atmosphere and another volume. The atmosphere is 14.7 PSIA at sea level; that 14.7PSI is measured between a vacuum and the atmosphere. I think you could use a differential pressure device and leave one port open to atmosphere.
     
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  14. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Unfortunately, there is no way I could have another port to the atmosphere, tubes going through the pipes are impossible (due to reeds), and to have an extra hole in the bag would require either dramatic DIY or a drastic change in pipe bag design.

    I'll have a look at some more sensors,

    Thanks again.
     
  15. strantor

    AAC Fanatic!

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  16. bertus

    Administrator

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  17. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    No I didn't, thanks Bertus.
     
  18. eceblr2011

    New Member

    Jul 8, 2011
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    You can check the pressure sensors from this link. See if any of these matches your requirement.
    http://sensing.honeywell.com/index....&N=3383+4294956248+4294853440&la_id=1&la_id=1

    I think you can use this pressure sensor: 1805-01A-L0L-B from Honeywell.
     
  19. Sparky49

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    Jul 16, 2011
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  20. strantor

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    I didn't read through the entire second datasheet because I became stumped on 1 question: How do you intend to do this? do you want the sensor inside the bagpipe, with wires coming out, or do you want a tube going into the bagpipe, attached to the sensor outside?

    the first one looks good. may even be able to mount it inside the bag. I like it because it has it's own vacuum reference inside, but the output starts at atmospheric pressure and goes up
     
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