Vol. 5 No. 6 December 1997
SOLID-STATE ELECTROLYTE OXYGEN SENSOR
Solid-state electrolyte oxygen sensor is gaining popularity in medical and aeromedical applications due to its fast response to satisfy physiological protection requirements, long operational and storage life, least maintenance and calibrating problems and easy interface to electronic systems. Solid-state electrolyte oxygen sensors are made from a number of ceramic metal oxides; but the most commonly used material is ZrO2.
ZrO2 is normally an electrical insulator but when doped with traces of di- or trivalent metal oxides (Y2O3) and heated above 600 oC, it becomes conductive due to the presence of oxygen vacancies in the crystal lattice. Since conductivity is determined by this specific mechanism, the electrical properties of this material are directly influenced by surrounding oxygen concentration and the material provides direct analogue electrical output. This sensor does not cross-couple with argon or other gases.
DRDO has successfully developed the above sensor for oxygen concentration measurements. The sensor consists of zirconia disc coated with porous platinum electrodes on both sides and electrical wires are taken out from the cell for measurements. One side of the disc is exposed to reference gas while the other to the gas in which oxygen concentration needs to be measured. The disc is placed in an alumina tube and is properly secured using high temperature ceramic seal. Alumina tube is held between a pair of NILO-475 diaphragms to provide stability against mechanical and thermal induced stresses. The nichrome wire wound on alumina tube forms the heater. Chrome-alumel thermocouple measures the temperature of operation. The electronic control unit based on 80196 microcontroller provides the required circuits for temperature control, temperature sensing and signal measurements.
The above sensor has been developed for the first time in India specifically for aeromedical applications. It will also find useful application in biomedical engineering.