A project to redefine the Kelvin, the basic unit of thermodynamic temperature, is making use of a formtester from metrology company Mahr Federal. The device, a MarForm MFU 110 WP, includes both tactile and optical sensors and provides accuracy into the nanometer range.
A project to redefine the Kelvin, the basic unit of thermodynamic temperature, is making use of a formtester from metrology company Mahr Federal.
The device, a MarForm MFU 110 WP, includes both tactile and optical sensors and provides accuracy into the nanometer range. It is being employed by the PTB (Physikalisch-Technischen Bundesanstalt) in Braunschweig, Germany, the counterpart of the NIST in the U.S. The goal of PTB’s portion of the project, conducted in conjunction with the General Conference on Weights and Meaures (CGPM), is to determine the Boltzmann constant K, the conversion factor between thermal and mechanical energy.
Precisely determining the Boltzmann constant requires defining absolute helium pressures. PTB accomplished this by using the reference formtester’s White Point optical stylus system to precisely measure the geometries of a pistons and cylinders in a pressure balance system at ambient pressure.
Capable of form and diameter measurements of precision mechanical parts with tolerances of less than 1 µm, the system is based on a concept of short coherence heterodyne interferometry working with two wavelengths. Typical parameters are roundness, straightness, parallelism, angle and diameter. The small optical probe is said to allow fast, non-contact measurement of small and hard-to-access geometries and provides optical contact at two different angles.
