Journal of Applied Crystallography

Volume 41, Part 2 (April 2008)

research papers

J. Appl. Cryst. (2008). 41, 373-376 [ doi:10.1107/S0021889808004652 ]

Convenient off-line error quantification and characterization of concentricity of two circles of rotation for diffractometer alignment

L. M. D. Cranswick, R. Donaberger, I. P. Swainson and Z. Tun

Abstract: To ensure concentricity of the [theta] -2 [theta] rotation stages, but with a very limited 2 [theta] range of rotation, an alignment technique using two dial gauges mounted at right angles to each other (X and Y axes) is described. The deflections of the orthogonal dial gauges are measured as a function of 2 [theta] , with their probes impinging on a cylindrical pin centred on the [theta] axis. The X and Y corrections required to bring the two rotation stages into concentricity can then be found using a least-squares fitting via a freestanding program or via the `solver' optimization within the Microsoft Excel spreadsheet software. The same dial gauges provide guidance for applying the required positional corrections. An Excel spreadsheet for determining the X and Y corrections via least squares has been deposited.

Keywords: neutron powder diffraction; off-line alignment; diffractometry; concentricity; circles of rotation.