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Typical Calibration Procedure of KOBA Ball Bar

  1. Calibration Object:
    The calibration object is an artifact (ball bar) which can be dismantled and is used for the calibration and interim checking of coordinate measurement machines.   The artifact consists of 10 distance bars and 11 ceramic spheres.
  1. Calibration Procedure:
    The ball bar was calibrated using a "calibration device for linear comparison standards" (DK No. 0372).  The measureing system of the device consists of a plan mirror laser interferometer.  It consists of the interferometer with a mobile probing component (Zeiss probe system) and a permanently mounted plane mirror.  A stabilized duel-frequency He-Ne laser is used whose wave length is corrected by the refractive index of air dtermined in accordance with the Edlen formula (parameter method).

    Traceability to the unit length "meter" is established by calibration of the overall measuring system, using parallel gage blocks of the nominal suze 50mm, official label 0274 PTB 98, of the nominal size 500mm, official label 111 PTB 96, and of the nominal size 1000mm, official label 110 PTB 96.

    The respective sphere mid-point distances of the different combinations, e.g. sphere 1/bar 1/sphere 2, sphere 2/bar 2/sphere 3 etc., were measured.
  1. Ambient Condiditons:
    The temperature, air pressure and humidity during measurement have been recorded on a data carrier in the calibration lab and can be communicated, if necessary.
  1. Measurement Results:
    The calibration results indicate the sphere mid-point distances of the combinations.

     

    Combination Sphere mid-point distance (mm) T 1 (°C)
    Sphere 0/bar 1-1/sphere 1 500.09940 20.05
    Sphere 1/bar 1-2/sphere 2 500.20707 20.03
    Sphere 2/bar 2-3/sphere 3 500.26838 20.04
    Sphere 3/bar 3-4/sphere 4 500.46535 20.04
    Sphere 4/bar 4-5/sphere 5 500.30931 20.05
    Sphere 5/bar 5-6/sphere 6 500.39038 20.04
    SPhere 6/bar 6-7/sphere 7 500.05702 20.03
    Sphere 6/bar 7-8/sphere 8 500.44678 20.06
    Sphere 8/bar 8-9/sphere 9 500.00810 20.09
    Sphere 9/bar 9-10/sphere 10 500.5244 20.08
    1 Temperature of ball bar during measurement (uncertainty = 0.03K)
    The lengths are specified relative to the reference temperature of 20°C and to the metrological condition of the ball bar during calibration.  A linear thermal expansion coefficient of 11.5 - 10-6 K1 was used to reduce the results of 20°C.

 

  1. Measuring Uncertainty:
    The measuring uncertainty for the sphere mid-point distances is U = 0.4µm + 2 * 10-6 = L, L = length of the ball bar.

The specification indicates the upgraded measuring uncertainty resulting from the multiplication of the standard measuring uncertainty by the factor k = 2.   It was determined in conformity with DKD-3.  The values of the measurement parameter lie within the specified range with probability of 95%.

 

 

The contents of the web-site are copyrighted © 1998, 2004, 2005, 2006, 2007 by Paul W. Marino Gages, Inc.  Reprint by permission only.
AMT®, American Modular Tooling® and Solutions® are trade names of Paul W. Marino Gages, Inc.
KOBA® is a registered trade name of Kolb & Baumann GmbH. of Germany,  The KOBA-Step® and KOBA-Check® are protected by patents.
Photos and illustrations contained herein may show items or components not distributed by Paul W. Marino Gages, Inc.
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Every effort has been made to insure the accuracy of this site.

Paul W. Marino Gages, Inc.
21300 MacArthur Blvd.
Warren MI 48089-3020  USA
Phone: (800) 528-9785 (North America) / (586) 759-2400
FAX: (800) 775-7829 (North America) / (586) 759-2423
  e-mail: pwminc@covad.net

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