Inductive sensors based on embedded coil technology for nanometric inter-segment position sensing of the E-ELT

The primary mirror of the E-ELT consists of a mosaic of 798 hexagonal mirror segments whose relative positions will be measured by 4524 so-called edge sensors. The main properties of these three axes edge sensors are nanometric precision, high linearity, low sensitivity to temperature and humidity fluctuations as well as high reliability. This paper presents the outcome of a development carried out by Micro-Epsilon in the framework of prototype activities launched by the European Southern Observatory several years ago. The performance of inductive sensors based on Embedded Coil Technology are presented as well as results obtained on representative operational conditions.