Smart Electrochemical Oxygen Sensor for Personal Protective Equipment

Self contained closed circuit rebreathers are life supporting breathing systems, where the exhaled gas is recycled by filtering CO₂ and replacing metabolized O₂. For the O₂ injection control galvanic O₂ sensors are used to measure the partial pressure of O₂. A malfunction of the sensors can lead to a gas mixture beyond life supporting limits which is life threatening. Galvanic O₂ sensors are often used in anaesthetic machines in hospitals. Also in this case, a malfunction of the sensors can cause severe injury to a person. It is obvious that such sensors are key elements in life supporting equipment and as such must be designed in order to achieve high functional safety. However these sensors are consuming sensors, and with that, will fail at a certain time. Failure modes include current limitation, non linearity, electrolyte evaporation or leakage, etc. Within this paper a novel low cost read out electronic circuit for galvanic O₂ sensors is presented, which allows not only digital readout, digital temperature compensation, on board storage of calibration and manufacturing data, but also can be used for performing voltammetry cycles to test the Pb anode for exhaustion. First measurements are presented and compared to data from a Solartron SI 1287 impedance analyzer, which is state-of-the-art in electrochemical sensor characterization.