Surface texture
The UKAS laboratory is able to measure all of the currently available parameters associated with surface texture, including German and French derivatives.
Roughness standards are calibrated to an uncertainty for the Ra parameter of ± 2% + 0.004 µm, which is the lowest currently available from any UK accredited UKAS laboratory outside of the National Physical Laboratory (NPL).
A tungsten carbide sphere is used to calibrate the Form Talysurf range of instruments. Its radius and roundness/sphericity are each calibrated to provide a high precision multi-purpose standard.
The ball is used to calibrate the instrument or as a confidence gauge to ensure its accuracy is maintained.
Straightness
Assessment of the straightness of a Talyrond column, or Talysurf radial arm, can be made using precision cylinders or optical straightedges respectively. The certified straightness of either, which has been obtained using the mechanical reversal technique of error separation, can be compared to that obtained from a measurement using the system in order to verify its geometrical accuracy.
Diameter and length
The laboratory is currently accredited for the calibration of spheres, plugs, rings, and length bars. Temperature corrected measuring techniques are used in conjunction with sophisticated control software to achieve uncertainties as low as ± 0.5 µm.
Polygons, prisms and angle gauges
The basic methods employed for angle measurement are either the accurate division of a circle using a high precision index table, or the generation of a known angle by means of a precision sine bar (angle generator) or rotary table.
The precision index table is used in conjunction with an autocollimator for the calibration of a polygons, prisms, and angle gauges. Measured errors are tabulated on the UKAS certificate, and by taking account of these errors during its use, a higher accuracy of measurement can be achieved by the user.
Autocollimators
A small angle generator jointly designed by Taylor Hobson and NPL is used in conjunction with Interferometrically calibrated gauge blocks for the calibration of an autocollimator. Both progressive and periodic errors are measured and certified, and knowledge of these errors can enable more precise use of the instrument by the operator.
Clinometers and levels
Block levels, clinometers and electronic levels are calibrated using sophisticated sine lever techniques. A Talyvel electronic level is calibrated using a Taylor Hobson small angle generator, and the user benefits from the ability to compensate for known errors when using the instrument.
Telescopes and collimators
The line of sight and displacement errors of a Micro Alignment Telescope are assessed using an optical wedge and fixed and variable focus collimators. Deviations are recorded on the UKAS certificate, providing the means for more accurate measurement. Micrometer and focussing accuracies are also verified using traceably calibrated scales and artifacts.
Flatness
Optical flats and straightedges are calibrated using a Zygo GPF phese shifting Interferometer to some of the smallest uncertainties that are commercially available. The on-site calibration of surface table flatness can be calibrated using a Talyvel electronic level in conjunction with analysis software to produce a 3 dimensional plot of the table surface.
Index and rotary tables
Various techniques are used for the calibration of rotary devices, and uncertainties can be as low as ± 0.3 seconds of arc.