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What's the difference between fine and coarse measurement?

  1. Jun 7, 2015 #1
    Would anybody pleas tell me whats the difference between fine and coarse measurement? I am reading a paper named "Electronic distance measurement-An introduction" in which fine measurement and coarse measurement is mentioned. here is the exact paragraph:

    "The transmitter includes a master oscillator, a digital divider (1: 100), a modulator and two infrared emitting diodes. The master oscillator (RTXO) produces the fine measurement frequency of 14.985400 MHz (- 15 MHz) corresponding to a unit length of 10 m. The coarse measurement frequency of 149.854 kHz (-150 kHz) is then derived by the divider."

    for-mentioned paragraph is an explanation about a Kern DM500 distance meter and describing whats going on inside.

    Any explanation in this regard is appreciated.

    Regards,Gilnaz
     
  2. jcsd
  3. Jun 7, 2015 #2
    I can think of two wildly different speculations.

    The Kern manual is pay only. Perhaps you should contact the company.
     
  4. Jun 7, 2015 #3

    meBigGuy

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    Gold Member

    Generally these things use phase shifts of reflected modulated light. Compare the transmitted signal with the phase of the reflected signal to determine the distance.

    If one uses wavelengths to measure distance, the a long wavelength (low frequency) will measure long distances with less accuracy and the short wavelength is used to get better accuracy.

    If you only use the the short wavelength, you could be off by a full wavelength. So the coarse/long wavelength tells you about where you are (within a short wavelength) and then the short wavelength makes the final measurement.

    This is predicated on the concept that the precision of the measurement of each wavelength is pretty much a constant "parts-per-wavelength". So if the short wavelength is 1/100th of the long wavelength, the short wavelength will measure 100 times more accurately (and the long wavelength will be able to measure 100 times longer distances without being multiple wavelengths).
     
  5. Jun 7, 2015 #4
    That was my first assumption. Then I got to thinking. What is this thing?

    My initial perusal was that it's a range finder for game hunting. (Not paramilitary use, that would be illegal I think.). What if the coarse measure was for large objects, let's say "deer". (Not AFVs, that would be illegal.) Then the fine measurement could be for duck hunting.

    This explanation isn't nearly as convincing as yours, but I couldn't rule it out without reading the costly manual. Of course I could be wrong about what this thing even is. Once again, a manual would be helpful. But while I'm willing to generously donate my time, I'm a tight fisted bastard.
     
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