Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Urgent- Physics coursework on sensing

  1. Feb 11, 2004 #1
    Urgent- Physics coursework on sensing (OCR B)

    The coursework is on using sound waves to measure the depth of water in a tank. I emit soundwaves using a sound generator and pick of the reflected wave with a mic. The original wave and the reflected wave are then shown on a osiliscope. I then need to use the speed of sound in air and some how find and combine that with the speed of sound in water? Also I have to measure the different interval time between the reflected wave and original wave?I dont know the speed of sound in water even after research and dont get how to combine them to use S=D/T. I need HELP PLZ!

    OCR B
    Last edited: Feb 11, 2004
  2. jcsd
  3. Feb 13, 2004 #2
    Re: Urgent- Physics coursework on sensing (OCR B)

    Well try this for speed of sound in water

    You can read time intervals off the oscilloscope. Try not using a 'sound generator'(?) make one large sharp sound (such as a hammer on a metal plate) and then you can see the original wave and the return wave... but it depends how good your oscilloscope is - can it record and display a trace?
  4. Feb 13, 2004 #3


    User Avatar

    Why would you need the speed of sound in air? Hmm... I suppose you may receive 3 peaks instead of 2 - one for the original, one for the wave reflected from the bottom of the pool, and one for reflection from the bottom.
  5. Feb 18, 2004 #4
    T = Timesoundcameback - Timesoundleft
    D = S * T
    S = 1404.3 + 4.7T - 0.04T^2
    speed works from 15-35 degrees C at maximum error of 0.18ms.

    use filters and a positive feedback op-amp to detect the pulses.
    use an LC filter to detect the apropriate frequency,
    use an op-amp with positive feedback and latch-up to detect sound, then measre the difference in time (using clock cycles and a counter) to figure out how much time has elepsed
    something like starting the clock (transister bias?) when the pulse leaves, then stoping it see above, when the pulse comes back (using op-amp).
    Sorry, i do programming and electronics, but not much else!
  6. Feb 19, 2004 #5
    Thankz for all the above its been a real help. Could PLZ on help on one thing. I dont know wot the following are and how they incorperate into my work:
    response time
    systematic bias or drift
    random variation
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook