Several radiometric and photometric measurements depend on high accuracy area measurement of precision apertures. Some apertures have sharp edges and are generally measured optically. At the Precision Engineering Division (PED) of the National Institute of Standards and Technology (NIST), we have developed a contact fiber probe for diameter and form measurement of micro-holes (holes of size 100 mm or larger). This probe exerts extremely small forces, under 5 mN, and can therefore be used on knife-edge apertures without causing edge damage. We have measured the diameter and roundness of three knife edge and one cylindrical aperture with this probe. The uncertainty in diameter ranges from 0.06 mm (k = 1) to 0.18 mm (k = 1). The uncertainty contributions from the probing system and machine positioning is together only 35 nm (k = 1). The largest contributors to the diameter uncertainty are the overall form (sampling uncertainty) and surface finish (mechanical filtering due to finite probe size) of the aperture.
Pub Type: Journals
aperture area, cylindrical aperture, contact measurement, fiber probe, knife-edge aperture, ultra low force