Sub nano measuring at commercial prices.
Eddy current displacement sensors capable of measuring
down to 0.08nm are being offered for less than £1,000 each.
The eddy NCDT 3700 family of sensors excite their coils at 0.5MHz.
Displacement is determined from changes in effective coil resistance
resulting from losses caused by eddy currents induced in the metal
target. They work with any electrically conducting, non-ferromagnetic
material. Resolution with an aluminium target is 0.000015% for
single channel and dual channel systems, or 0.000008% for
Measuring ranges are 0.5, 1, 1.5, 3 or 6mm. Repeatability figures
are given as <0.001% and 0.0005% for the two types and unearities,
+6% and +1%.
To give an idea of scale, 0.08nm is slightly more than the distance
between two bonded hydrogen atoms or about one third the distance
between two bonded iron atoms. Vendor Micro-Epsilon is careful to
say that "measurement results down to 0.O8nm have been
established" so such extreme precision sounds as if it is quite
difficult to achieve. Nonetheless, the transducers are successfully
employed in applications such as wafer positioning in semiconductor
manufacture; positioning of exposure units in photolithography; and
mirror positioning in the VLT telescope.
The European Southern Observatory's VLT is based in Paranal in
Chile and consists of four 8m telescopes. Adaptive optics enables
images to be obtained with a resolution of 0.07 arc seconds,
comparable to the quality of those sent back by the Hubble Space
Telescope. Other uses include monitoring the air gap in magnetic
bearings and machine tool spindle movement, and the alignment
of stepper systems.
For further information, please contact:-
Micro-Epsilon UK Ltd.
Telephone: +44(0)151 355 6070
Fax: +44(0)151 355 6075