Fibre-Optic Reflection Nanometric Displacement Measurement Systems Principles of Operating, Construction, Investigation

Abstract

A fibre-optic real displacement nanometer in comparison with its prototype has twice increased sensitivity and reached 0,560 mV×nm-1 and the linear part of the measurement characteristic of ±60 mm, and resolution as low as 2 nm. This is achieved by specific distribution of the fibre ends in a measurement head and special signal control by attenuators. The sensor consists of a pulsed LED light source, one light transmitting fibre, a pair (A and of identical receiving fibres and photodetectors that detect light reflected from the surface being measured. The differential signal (A-B) of the detectors is proportional to the absolute displacement of the surface relative to zero position. Light intensity variations of the source and the reflectance change of the surface and influence of temperature are compensated when the (A-B) signal is divided by the sum (A+B). The nanometer offers the advantages of increased sensitivity and the linear part of the measurement characteristic, high temperature and temperature interval operating, better precision (0,03 %) and portability, no electrical and magnetical interference, simplicity, and low cost. It can be used in laboratory instruments, dynamometers, dilatometers, torque sensors, membrane and bellow pressure sensors, accelerometers, and vibrometers.