Calibration characteristics of a video dimension analyser (VDA) system.

A comprehensive calibration and error analysis of a video dimension analyser (VDA) system was carried out to determine the effects of various parameters relevant to actual test conditions on the characteristics of the system. The parameters considered were: (1) varying distances or angles between the test specimen and the camera; (2) refractive effects of glass tank and physiologic solutions; and (3) dynamic response of the VDA system. The error analysis shows that, at low strain levels, the strain computed by the VDA is sensitive to camera placement and orientation as well as the media through which the object is observed. Very large errors can occur at small nominal strains, depending on the system parameters (e.g. 80% error at 1% nominal strain for one set of parameters). At higher strain levels, the sensitivity of the system is reduced, and the strain computed by the VDA system approaches the nominal strain (10% error at 10% nominal strain).