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  1. #1
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    Default Interesting air flow sensor developments

    Developments in drone technology has resulted in some interesting new mini sensors arriving on the scene.
    Air speed sensors kits like this small pitot tube, pressure sensor and ADC look like they might be worth exploring for dust extraction systems.
    digital airspeed

    The kits are available on ebay for about $70
    Pixhawk PX4 Digital Airspeed Sensor Air Speedometer with Differential Pitot Tube | eBay

    Their geometry means they don't immediately suit duct air speed measurements, and they need some sort of a microcontroller like an arduino or similar to access the data.

    On the plus side they are supposed to measure air speeds up to 17600 FPM which is pretty impressive.
    The ADC used in the kit has 14 bit (nominally 43 FPM) resolution which is impressive but no accuracy spec is provided.

    Could be my next Arduino project?

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  3. #2
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    Would you be able to use the provided pitot tube or would a bent one be needed too?

    Pete

  4. #3
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    Interesting kit. Good find Bob. That pitot tube looks fairly small, have you seen dimensions for it? Scaling the photo it looks like maybe 5mm or less. That could be useful.

    Quote Originally Posted by BobL View Post
    On the plus side they are supposed to measure air speeds up to 17600 FPM which is pretty impressive.
    The ADC used in the kit has 14 bit (nominally 43 FPM) resolution which is impressive but no accuracy spec is provided.
    The Data Sheet for the sensor reveals a lot. The total error band is specified to be ±1% of span. Span for the P/N used in the kit is 2PSI so TEB is ±0.02PSI or ±0.55"wg or ±138Pa. Obviously you would set zero in software and hope for good linearity.

    The total span is covered by 80% of the total 14 bits, so 6445 counts/PSI for a resolution of 1.05Pa or 0.0042"wg. The FPM resolution varies widely over the range because of the square law relationship between pressure and velocity.

    The sensors are readily available in distribution as well as on Ebay. Based on the data sheet it should be possible to build a high quality manometer with data logging and processing for not a whole lot of money. I'm starting to smell a new project too.

    Again, nice find Bob!
    Dave

  5. #4
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    Quote Originally Posted by QC Inspector View Post
    Would you be able to use the provided pitot tube or would a bent one be needed too?

    Pete
    As I said above "Their geometry means they don't immediately suit duct air speed measurements"

    A bent pitot tube would be better since it enables easy orientation directly into the air flow and being slimline can be inserted though a small hole in the side of the duct. A straight pitot tube requires some sort of right angle support mechanism to support the tube and the small pressure line hoses. If the tube is not long enough this mechanism may also affect the air flow.

    It will require someone to buy one and test it out.

  6. #5
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    Quote Originally Posted by dmorse View Post
    Interesting kit. Good find Bob. That pitot tube looks fairly small, have you seen dimensions for it? Scaling the photo it looks like maybe 5mm or less. That could be useful. The Data Sheet for the sensor reveals a lot. The total error band is specified to be ±1% of span. Span for the P/N used in the kit is 2PSI so TEB is ±0.02PSI or ±0.55"wg or ±138Pa. Obviously you would set zero in software and hope for good linearity.
    The kit I looked at said;
    Featuring a Measurement Specialties 4525DO sensor, with 1 psi measurement range (roughly up to 100 m/s or 360 km/h or 223 mp/h), the Pixhawk Airspeed Sensor Kit enables a resolution of 0.84 Pa, with data delivered at 14 bits from a 24 bit delta-sigma ADC.
    I could not see how the different pressure ranges were indicated by any part numbers on the data sheet.
    The total span is covered by 80% of the total 14 bits, so 6445 counts/PSI for a resolution of 1.05Pa or 0.0042"wg. The FPM resolution varies widely over the range because of the square law relationship between pressure and velocity.
    Good point.

    The sensors are readily available in distribution as well as on Ebay. Based on the data sheet it should be possible to build a high quality manometer with data logging and processing for not a whole lot of money. I'm starting to smell a new project too.
    Will you be considering the kit or just the transducer?

    I used a AUS$28 MPXV4006DP (Max 6kPa) pressure sensor on my DC pressure monitor running through a 12 bit (M0) Arduino
    Some details here. DC temperature/pressure meter

    For AUS$18 there is a nice 10kPa sensor (plus lots of others)
    https://au.element14.com/nxp/mpxv501...0-0/dp/2080495

    These things a probably even cheaper in the US.

  7. #6
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    Quote Originally Posted by BobL View Post
    The kit I looked at said;
    Featuring a Measurement Specialties 4525DO sensor, with 1 psi measurement range (roughly up to 100 m/s or 360 km/h or 223 mp/h), the Pixhawk Airspeed Sensor Kit enables a resolution of 0.84 Pa, with data delivered at 14 bits from a 24 bit delta-sigma ADC.
    I could not see how the different pressure ranges were indicated by any part numbers on the data sheet.
    One of the photos on your ebay link has a good view of the p/n. The p/n decoder is the last page of the data sheet. 4525D 5AI 001D decodes to 5V, 10% to 90% output, Address 0x28H, 1PSI Pressure Range, Differential. No marking is needed to indicate package style.

    Will you be considering the kit or just the transducer?

    I used a AUS$28 MPXV4006DP (Max 6kPa) pressure sensor on my DC pressure monitor running through a 12 bit (M0) Arduino
    Some details here. DC temperature/pressure meter

    For AUS$18 there is a nice 10kPa sensor (plus lots of others)
    MPXV5010DP - NXP - Pressure Sensor, Differential, 4.4 mV/kPa

    These things a probably even cheaper in the US.
    Probably just the transducer. I'm familiar with the NXP parts. What I like about the TE unit is the digital interface. I like to avoid analog runs for noise reasons and use WIFI to communicate. My current favorite board is the NodeMcu but the A/D in it isn't very linear so the I2C interface looks useful.
    Dave

  8. #7
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    Quote Originally Posted by dmorse View Post
    One of the photos on your ebay link has a good view of the p/n. The p/n decoder is the last page of the data sheet. 4525D 5AI 001D decodes to 5V, 10% to 90% output, Address 0x28H, 1PSI Pressure Range, Differential. No marking is needed to indicate package style.
    Thanks

    It's also that you said it was a a 2 psi sensor?

    Probably just the transducer. I'm familiar with the NXP parts. What I like about the TE unit is the digital interface. I like to avoid analog runs for noise reasons and use WIFI to communicate. My current favorite board is the NodeMcu but the A/D in it isn't very linear so the I2C interface looks useful.
    I agree about the noise issue. With my DC pressure sensor I have the sensor right alongside the MCU and run 1/4" irrigation tubing the 3m from the sensing point to the sensor.

  9. #8
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    Quote Originally Posted by BobL View Post
    It's also that you said it was a a 2 psi sensor?
    Per the last page of the data sheet the Pressure Range is 1PSI. On page 8 Pmin is defined as -Prange or -1PSI. Pmax is Prange or 1PSI. On page 5 Pmin gives an output count of 1638. Pmax yields a count of 14746. That's 13,108 counts for a 2PSI span or 6554 counts for 1PSI or a resolution of about 1.05Pa.
    Dave

  10. #9
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    The Pixhawk sensor and pitot tube turned up today.
    Boy is it small.
    The LR44 cell has nothing to do with it , I just included iti in the photo to show scale.

    No I'll have to do something wth it.
    IMG_4285p.jpg

  11. #10
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    Quote Originally Posted by BobL View Post
    The Pixhawk sensor and pitot tube turned up today.....
    Bob, if you have the opportunity could you check the diameter please?

    Thanks.
    Dave

  12. #11
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    Quote Originally Posted by dmorse View Post
    Bob, if you have the opportunity could you check the diameter please?

    Thanks.
    I assume you mean of the pitot tube? if so 4.0 mm

  13. #12
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    Quote Originally Posted by BobL View Post
    I assume you mean of the pitot tube? if so 4.0 mm
    Yes, that's it. That is nice and small. Thank you!
    Dave

  14. #13
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    Perhaps mounting along the lines of an aircraft pitot tube. The teardrop shaped mast would disturb the air the least and help align the tube in the duct. It could be made of wood, machined from metal or plastic, cast in resin or 3D printed. Can the two tubes at the back of the block be bent to 90º from the main tube? It would make the mast a little smaller if they can.

    A couple picture links of what I am thinking of.

    6a95a950-f0a6-4d22-a5ca-81896f62e96a.jpg

    RV PITOT TUBE.jpg

    Pete

  15. #14
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    Quote Originally Posted by QC Inspector View Post
    Perhaps mounting along the lines of an aircraft pitot tube. The teardrop shaped mast would disturb the air the least and help align the tube in the duct. It could be made of wood, machined from metal or plastic, cast in resin or 3D printed. Can the two tubes at the back of the block be bent to 90º from the main tube? It would make the mast a little smaller if they can.
    I doubt the metal tubes can be bent but the connected silicone tubes are of course easily bent and could be housed inside an appropriate streamlined housing. The first thing I want to do is just see if I can data out of it. This could take some time as my gout has eased a little and now have heaps of catch up jobs to attend to.

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