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A simple method for high-precision calibration of an angle encoder using an electronic nulling autocollimator



Lawrence T. Hudson, M N. Kinnane, Albert Henins, M H. Mendenhall


We describe a simple method for high-precision rotary angle encoder calibration. By using a redesigned electronic nulling autocollimator, a mirrored-polygon artifact is calibrated simultaneously with determining the encoder error function over a rotation of 2π. The technique is applied to the NIST vacuum double crystal spectrometer, which depends on precise measurement of diffraction angles to determine absolute x-ray wavelengths. By oversampling, the method returned the encoder error function with an expanded uncertainty (2σ) of ±0.004 second (angular). Knowledge of the error function permits the instrument to make individual encoder readings with an accuracy of 2σ = 0.06 second, which is limited primarily by the least count and noise of the encoder electronics. While the error function lay within the nominal specifications, it differed from the intrinsic factory curve, indicating the need for in situ calibration in high-precision applications


angle encoder calibration, nulling autocollimator, precision goniometry


Hudson, L. , Kinnane, M. , Henins, A. and Mendenhall, M. (2015), A simple method for high-precision calibration of an angle encoder using an electronic nulling autocollimator, Metrologia, [online], (Accessed May 25, 2024)


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Created March 9, 2015, Updated November 10, 2018