Low drift fibre optic pressure sensor for oil field downhole monitoring

Pressure sensors made of silica optical fibre change their zero offset (dri ft) by large amounts when exposed to fluids under high temperature and pres sure. Molecular water diffusion from the fluid into the silica is the cause of this drift. The effect of commercially available 'hermetic' coatings in preventing water ingress into fibres under such extreme conditions has bee n investigated. Application of the most effective coating to a pressure sen sor has improved the drift late by a factor of 200.