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ULTRASONIC DISTANCE SENSOR OF RANGE 0.1milimeter — Parallax Forums

ULTRASONIC DISTANCE SENSOR OF RANGE 0.1milimeter

gaurav89gaurav89 Posts: 4
edited 2012-12-16 17:42 in General Discussion
is there any ultrasonic distance sensor which can measure the distance with precision of 0.1mm. if not then whether it can be manufactured or not. is there any limitation on distance measured by ultrasonic sound sensor. what are the reasons behind those limitations.
what best precision we can get using ultrasonic distance sound sensor.

Comments

  • msrobotsmsrobots Posts: 3,709
    edited 2012-12-14 19:13
    I am no expert here but t has to do wth the speed of sound and the wavelength. the time between sendng the pulse and receving the echo is to short to mesure.

    So things like PINGs can work with inches, but below that - will not work.

    Enjoy!

    Mike
  • gaurav89gaurav89 Posts: 4
    edited 2012-12-14 19:47
    hello Mike

    mike i wrote my question wrongly earlier. actually my question is can we get the precision of 0.1mm in measuing distance. what precision generally given by ultrasonic sound senser?

    thanks
    Gaurav
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-12-14 19:48
    With a typical 38 kHz transducer, the wavelength of that sound in air is about 9mm. Divide that by two, since the "ping" covers the path twice, and you've got 4.5mm. That would be a ballpark figure for the limiting uncertainty in any distance measurement.

    -Phil
  • msrobotsmsrobots Posts: 3,709
    edited 2012-12-14 20:02
    I guess you may come down to cm but never to mm

    and repeated mesurements will give slightly different results.

    I am experimenting with different sensors to ths out for my (delayed) rover-project.

    Overall the results are not good. All used Sensors vary much and give unstable results. By now I use GPS, PING and the Infrared Sensor from Parallax.

    You need to do a lot in software to 'clean up' your data and work with 'changes over time' to get more stable and usable results.

    As often it depends on what you need to do. Sometimes Ultrasonic works well sometmes Infrared is better. Just describe what you want to do and maybe some other sensor will do better.

    Ah ... by the way ... welcome to ths forum ...

    If you descibe what you need to measure you will find a answer here. Ths forum is full of very helpful people.

    so

    Enjoy!

    Mike
  • jmgjmg Posts: 15,183
    edited 2012-12-14 22:10
    gaurav89 wrote: »
    is there any ultrasonic distance sensor which can measure the distance with precision of 0.1mm. if not then whether it can be manufactured or not. is there any limitation on distance measured by ultrasonic sound sensor. what are the reasons behind those limitations.
    what best precision we can get using ultrasonic distance sound sensor.

    As others have mentioned, the wavelength gives one indicator, but there is also the reflectance variation of what your echo comes from, and temperature...

    See
    http://en.wikipedia.org/wiki/Speed_of_sound#Tables

    Thus it is not enough to ask for 0.1mm, you need to specify the distance, and surface(s)

    Temperature alone, will vary 1.71% / 10'C, and so 0.1mm of error accumulates in just 5.8mm of path (!)

    The wavelength itself does not have to be a hard limit, as you can take the envelope sampled at many points, and apply some DSP to decide a ratio threshold.

    If you can run differential (use a known distance and same-reflectance), then you can expect to drive precision further, (you can now correct for Temperature and Humidity), but this is no longer a simple 'point at anything' system.
  • prof_brainoprof_braino Posts: 4,313
    edited 2012-12-15 06:37
    gaurav89 wrote: »
    hello Mike

    mike i wrote my question wrongly earlier. actually my question is can we get the precision of 0.1mm in measuing distance. what precision generally given by ultrasonic sound senser?

    thanks
    Gaurav

    Do you want to measure items closer than 9mm with a precision of 0.01mm? Or do you want to measure distant object with that precision?

    There may be a way to do both, but would require a little more work than a stock ping sensor and a single pulse.

    If you can list out your specific requirements in detail, we can give it a look
  • gaurav89gaurav89 Posts: 4
    edited 2012-12-16 16:59
    hi,
    i am thinking to make a screen touch using sound sensor. the arrangement of system will be like this:-
    there will be two microphone and one speaker and all three will be having synchronized timer. the microphone will be installed in stylus and two speaker on two corner of screen. whenever stylus is touched to screen it will encrypt its timer value in sound waves and play the same. when it will be received by microphones, both microphone will check their timer value and also decrypt the time value sent by speaker by sound wave and find the time it take to reach upto microphone. then distance b/w microphone and stylus can be calculated. and we know the distance b/w both the speaker. so using triangular properties we can find the point of touch.
    what do you think about the feasibility of this project. and what challenges are there?
    thanks
  • jmgjmg Posts: 15,183
    edited 2012-12-16 17:42
    gaurav89 wrote: »
    what do you think about the feasibility of this project. and what challenges are there?
    thanks

    The problem is a finger is a small target, and one with varying angles.

    However, something quite close to what you want, is already commercial
    See
    http://en.wikipedia.org/wiki/Touchscreen#Surface_acoustic_wave
    - rather than send sound via air, these send it thru the screen membrane, and sense the actual touch dampening effect.

    Other designs I know of use line-scan ( 1 pixel x many) cameras, to image the touched point.
    Light waves are far shorter than Audio waves.

    Another variant is here
    http://en.wikipedia.org/wiki/Acoustic_tablet
    - but notice this uses an active stylus as the emitter, and multiple microphones.
    Thus this avoids trying to find reflections.
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