Solid-state electrolyte sensors for rebreather applications: a preliminary investigation

Recently developed prototypes of zirconium dioxide and NASICON-based micro solid-state electrolyte oxygen (O2) and carbon dioxide (CO2) sensors were tested for their potential suitability in rebreathers. The O2 sensor has a quasi-indefinite lifetime, whilst that of the CO2 sensor is approximately 700 h. This is a preliminary report of a new technological application.

The O2 sensor was tested in a small pressure chamber to a partial pressure of oxygen (PO2) of 405 kPa (4 bar). The CO2 sensor was tested up to 10 kPa CO2. The response times to a step change of pressure were measured, and cross-sensitivity for helium tested using trimix. A rebreather mouthpiece was modified so that breath-by-breath gas recordings could be observed. Power consumption to heat the sensors was measured.

The O2 sensor demonstrated non-linearity, particularly above 101.3 kPa (1 bar) PO2, whereas the output of the CO2 sensor showed an inverse logarithmic relationship. Cross-sensitivity to helium was observed. The mean t90 response times were 90 (SD 10) ms for the O2 sensor, and 100 (SD 10) ms for the CO2 sensor. Breath-by-breath recordings showed slight damping of the CO2 trace due to electronic filtering. Power consumption was 1.5-2 W per sensor.

The fast response times would allow accurate breath-by-breath measurement. Even though the O2 sensor has a non-linear response, measurement is possible using multi-point calibration. Further design is necessary to allow trimix to be used as the diluent. A major disadvantage is the high power consumption needed to heat the sensors to high temperatures.