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Ping aneometer — Parallax Forums

Ping aneometer

jgs1968jgs1968 Posts: 3
edited 2011-07-29 16:28 in Robotics
I would like to measure air velocity (as a % of full flow.... or no flow) in a air duct. I know that there are ultrasonic meters out there.

I am wondering if anyone has built the Ping module code and installation design.

I am proposing to transmit from the sendor outside the duct to a two corner reflector aiming the bounce at the return sensor within the duct. Is the PING sensitive enough to sense velocity changes due to changing fan speeds at 20cfm to 100cfm.

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-07-23 18:28
    I'm pretty sure the Ping module can't do this.

    Actually I don't think any ultrasonic sensor can detect the speed with the setup you describe.

    To sense airflow, you'd need the sending and receiving units in different location from one another. If you bounce the signal off a reflector it will take the same time no mater the speed of the air flow since it would go faster in one direction but slower in the other.

    You'd want one of the sensors "down wind" from the other. (Not that I know how to build the needed circuitry.)

    Duane
  • PublisonPublison Posts: 12,366
    edited 2011-07-23 18:37
    The Ping Sensor can only detect distance to solid objects. I don't think it can detect air flow.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2011-07-23 18:42
    Parallax sells these weather proof transducers.

    You could use one down wind from the other to make your sensor.

    BTW, Welcome to the forum.

    Duane
  • jgs1968jgs1968 Posts: 3
    edited 2011-07-23 20:17
    Thanks everyone. I'll share my reasoning.
    A 'hot-wire' aneometer sounds exotic, and is used commonly in car intake manifolds as 'air-mass' sensors.
    But you can demo the same concept with a common light bulb's exposed filiment. Air movement cools the wire, changing the resistance and results in a change in current.

    But a hot wire in a dusty air duct is not good.

    Reading up in ultrasonic aneometers (UAs) reveals that they use a transmitter and reciever. the sound waves sent will arrive at the reciever faster in still air than moving air.
    the sonic in ultrasonic is simple sound waves, and effected by wind pushing them around. Waves sent into a wind will arrive more slowly than into still air.
    You will see roadside UA's at roadside weather stations. They are the two goofy arms sticking out.

    I guess that transmitter frequency and receiver sensitivity will be the issues.

    As far as hardware mounting, I am thinking that with PING, to transmit in protected air to the reflector, and the reflector bounce the wave into the duct, and again back to the reciever.
    In still air, a fixed value of some sort would be returned to UNO. When air is moving, that value would change, resulting in some new value. That new value would tell UNO that air is no longer still.
    What that value is, or how much range and sensitivity is available IS an issue

    It seems like an interesting experiment, and fairly easy to demonstrate. I am wondering if anyone else did.

    And thanks for the link Duane, I'll be looking at that.
  • FranklinFranklin Posts: 4,747
    edited 2011-07-24 16:51
    The ping is not designed to do this. Although it does use ultrasonics, it uses them differently that an ultrasonic anemometer.
  • Ed TEd T Posts: 50
    edited 2011-07-28 08:52
    You should just be able to remove the ultrasonic transmitter from the Ping and reconnect it with a length of wire. This way you can get some distance between the transmitter and receiver and have your sound pulse travel in only one direction in the airflow. Do this with the transmitter since it is operating at +/- 5V. The receiver is sensing small signals and will be susceptible to noise.
    -Ed
  • Ed TEd T Posts: 50
    edited 2011-07-28 09:07
    My above comment should not be taken to mean it will work as an anemometer. I don't know the details on their operation. I would be worried about the sensitivity you need if you are trying to measure a 20mph change in the 750 mph speed of sound (<3%). Maybe Franklin can provide a few more details on how the ultrasonic anemometer works. Maybe it is measuring phase of the received sound wave for better accuracy?
    -Ed
  • Dave HeinDave Hein Posts: 6,347
    edited 2011-07-28 12:24
    Ed, it seems like your suggestion should work. In normal use, the distance is T*Vs/2, where Vs is the speed of sound and T is the time between the transmitted pulse and the received pulse. If the transmitter and receiver are separated by a known distance, then the velocity would be determined by D/T. The air speed would be V - Vs, where V is the measured velocity. You would need to adjust for the temperature since the speed of sound is faster at higher temperatures.
  • jgs1968jgs1968 Posts: 3
    edited 2011-07-29 16:28
    Thanks for the input, everyone. I was really hoping that someone would say "Oh, Yeah... do this!"

    Thanks for the formulas. I guess it always helps to start at the beginning! I should be able to see how distance variability due to the 40Khz 'window' might be effected by airflow.

    I know that the PING was not intended for this use, and was hoping that I had discovered an unintended capability.

    I am doubtful about removing the transmitter from the board. It seems like the documentation suggested that sync between send and receive were a critical function of the board. Perhaps working with the two transducers will work.

    My app proposes to push about 20 to 70CFM down a 6' round duct. I want to be able to confirm that a given cfm is exiting the far end on a real time basis.

    I'll keep an eye on this thread for awhile. The comments so far have been helpful.

    Thank you everyone
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