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Differential pressure sensor project? — Parallax Forums

Differential pressure sensor project?

dcbrowerdcbrower Posts: 1
edited 2013-09-06 17:31 in Accessories
I'm looking to build a pitot-tube style windspeed sensor. This instrument takes the difference in pressure between an open tube facing into the wind and another tube lying across the wind. Does anyone have any experience building a project like this?
I was thinking of using one of the MPX2010-series differential pressure sensors. Is that a good choice, or is there a device that would interface better with the BASIC Stamp Homework Board?
Many thanks for your input!

Comments

  • Tracy AllenTracy Allen Posts: 6,664
    edited 2013-09-05 09:00
    Welcome to the forums!

    That would be a nice project, but there are a couple of catches I can see. The MPX2010 measures pressures from 0 to 10 PSI, whereas the differential pressure of a pitot tube will be much less by a large factor. Since this is for a windspeed sensor, consider the pressure you might see from a pitot tube facing into the wind in dry air at sea level:

    30m/s = 67mph ==> 55mmH2O = 539 Pa = 0.078 PSI

    Compare that to the 10psi scale of the MPX2010, a mismatch. There is a square root, not linear, relation between pressure and velocity, so lower windspeeds will give even less than proportional pressure.

    The output of the MPX2010 is in any case a small voltage, a change of only 25 mV over its full span, so your interface would need to be sensitive at the microvolt level.

    I'm not sure what to suggest as an alternative pressure sensor. Maybe someone else will have an idea about that. The homework board does not have an analog-to-digital converter built in, so it would be nice if you can find a pressure sensor that provides a digital result directly. Maybe something that is sensitive at the level of blood pressure measurements.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-09-05 09:14
    There are sensors made for this type of thing. I know I purchased one in a recent Digi-Key order but I haven't tried it yet. I'll find the part number and post a link soon.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-09-05 09:23
    Here's a link to the sensor I had in mind. Its range is -0.3 psi to 0.3 psi.

    It looks like it outputs a voltage so you'd need some sort of ADC chip to read from a Basic Stamp.
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2013-09-05 19:30
    That seems to be a good possibility, Duane, not too expensive as such things go. I found one from Sensirion that has a digital (i2c) interface, very sensitive ranges (±500 Pa standard), but it runs $100.

    ±0.3PSI is the same as ±2000Pa. A 12 bit converter could read it down to 1Pa resolution. It would benefit from even higher resolution (& precision) on the low end, due to the pressure being proportional to the square of windspeed.
  • xanaduxanadu Posts: 3,347
    edited 2013-09-06 17:31
    I have used this one - https://store.3drobotics.com/products/airspeed-kit-with-mpxv7002dp (same as Duane's but with the tube)

    The pitot tube design works better than what you would see conventionally with the side facing static port.
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