DrägerWerk in Lübeck, Germany and Xensor have together developed the sensing heart of a revolutionary oxygen sensor. The measurement is based on determination of the thermal conductivity of the gas surrounding the silicon chip, which yields a measure for the concentration of oxygen.
Derived from the standard thermal conductivity gauge XEN-3880, a special has been developed for Dräger in which the chip is mounted on a ceramic base plate that also contains a PTC-resistance and a separate heater resistance, to allow thermostatting of the base plate, thus improving the measurement accuracy.
Around the chip a flow channel has been created using specially formed ceramic parts, allowing the gas to be led past the sensor without actually flowing over the sensor surface. In this way, a fast response time has been achieved for refreshing the gas composition around the sensor, while avoiding that the sensor acts as a flow sensor. Thus, a true and accurate thermal conductivity measurement is carried out.
Oxygen concentration is determined at a rate fast enough for breathing applications at a resolution of the order of 0.5 % oxygen concentration. This is achieved in the presence of anaesthetic gases.