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accurate angle measurement

Discussion in 'Electronic Design' started by mario, Sep 6, 2006.

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  1. mario

    mario Guest

    Hi everybody,

    Can anyone suggest me some idea for measuring angles up to seconds? or
    Where can I find the principle used by theodolites in measuring angles?

    Thanks a lot
  2. That is a bit little information. There can
    be optical masks with micrometer resolution.
    Is your problem a scientific problem to be
    solved once, a technical problem to be
    solved repeatedly or a business problem to
    be solved cheapest in numbers.

  3. default

    default Guest


    Theodolites implies angle - more of less.

    A rate gyro, on a chip?
  4. Joerg can make it cheaper :)

  5. Fred Bartoli

    Fred Bartoli Guest

    martin griffith a écrit :
    But only Philips and Infineon make that dreadfully required component.
  6. mario

    mario Guest

    Rene, I want to measure the angle position of a 4~6 cm radius disc.
    Does it help?

    Rene Tschaggelar ha escrito:
  7. Dave

    Dave Guest

    Avago (was Agilent (was HP)) make some quite nice absolute and incremental
    encoders (14 bit). ( If you have real money there are some laser based
    encoders that work down to a few arc seconds, and also some rotary
    transformer based solutions. )

    You need to specify:-

    Absolute or Incremental ?


    Angular speed and acceleration?

    Do you require 360 degree revolution ?

    How much do expect to spend ?

  8. Guest

    Quartz crystal cut angles are measured to seconds of arc to get optimum
    temperature coefficient. Xray defraction and rugged mechanical
    construction are key elements.
    For a cheap system two a radial gratings and count the fringes as the
    transparent upper grating is rotated over a lower grating could do it.
  9. Guest

    A little calculation shows that a pointer/scale one-arcsecond system on
    the disk requires alignment
    precision (and also axis-of-rotation position) of 0.14 microns. That's
    not possible
    with simple light-readout systems.

    For reference, a CD squeezes about 6170 bits into one degree of disk
    with good diffraction-limited optics and lotsa tricks (like
    servo-controlled tracking
    mechanisms). That's 1.7 bits per arcsecond of rotation.

    One can just about use lightbeam interferometry to measure a triangle's
    sides to this
    precision, but it's not gonna be a simple measurement.
  10. mario

    mario Guest

    Hi Dave,

    My needings are: incremental, accuracy half second or second at most,
    speed 1.5 revs/sec at most, yes 360 degree, $ 500 to 700 approx

    Dave ha escrito:
  11. Steve

    Steve Guest

    Add a 'k' to those values and you just might do it.

    Do you really mean seconds ? To put what you've said in context, that's
    less than the width of a motorway measured from the centre of the earth.

    - Steve
  12. John Perry

    John Perry Guest

    Another way: you're asking for 1 part in 1296000 _accuracy_. Even that
    kind of _resolution_ is not easy.

    John Perry
  13. joseph2k

    joseph2k Guest

    Apparently you have never worked with any high resolution angle measurement
    systems. I can do that using 1950's technology, all gears and some tubes
    as needed. Back in the 1970 i saw 30 bit per revolution systems, i expect
    that better can be readily achieved today.
  14. A rotary transformer based solution is the Inductosyn (Farrand Controls It's typically 360 speed (cycles per rev).

    To encode the Inductosyn position, you can get an Inductosyn to digital
    converter or design your own.

    In a former life we did our own encoder. Using a 16 bit ADC, we encoded
    position to 18 bits per degree, or about 0.01 arc-seconds. Accuracy
    however was not better than the Inductosyn, which was about 0.5 - 1
    arc-second for IIRC a 12 inch diameter model. Achieving this level of
    accuracy required the use of patented calibration techniques.

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