Recent measurements with Ru²⁺ oxygen sensors using doped sapphire crystals both as a calibration aid and an integral temperature sensor.

Description/Abstract

Recent measurements are presented, using an improved, real-time, all-optical sensor for simultaneous measurement of dissolved oxygen and temperature. The sensor has a small Cr³⁺ - doped sapphire (ruby) thermal monitoring crystal mounted at the probe tip, to which is bonded a Ru³⁺-based oxygen-indicator membrane. The probe may be interrogated in real-time, using, for both temperature and oxygen monitoring, the same combination of blue LED, light source, optical filter set, photomultiplier detector and digital processor. The ruby crystal also provides a fluorescent intensity reference, for possible on-line self-testing of the interrogation hardware. By examining the relative intensities from ruby and the membrane, mechanical damage, detachment or photo-bleaching of the sensing membrane may also be recognised. Recent developments of our novel, Ti³⁺-doped sapphire fluorescence-lifetime calibration probe are reported. These confirm that the flu
orescence lifetime of the probe can be thermally controlled-in a reliable manner. This calibration probe then allows multi-point calibration of Ru³⁺-chemical sensors.