The limiting performance characteristics of con-focal chromatic aberration displacement sensors are angular tolerance
and the gauge range over which an output is provided. The sensor selected in this study is used to measure groove
profiles in early recorded surfaces. The sensor is used in a 3 dimensional cylinder scanning system for the measurement
of wax cylinder recordings, where the 3 dimensional data is used to create a map of the measured surface for archival
purposes. The generation of the map allows the sound recorded on the surface to be decoded without physical contact to
the surface. It has been shown in a previous study that data resolution of 10-20nm are required for this application, and
that the relationship between the data output and the surface incline is critical to system performance. To understand the
relationship with surface slope the sensor is used here in a study of the measurement of calibration ball surfaces, and
follows a previous study on machined grooves with known angular properties.
In this study a range of calibration spherical surfaces are used to investigate the relationship between the sensor output
and measurement parameters, including the distance between the sensor optical head and the surface. A linear least
squares method is used to evaluate the 3D radius of the measured surfaces, and this is used as a parameter to evaluate the
The results show that there is a low level of systematic form error typically below 1&mgr;m, but that this error has a
significant impact on the evaluation of the radius. Recommendations are made on methods for optimisation of sensor performance.