Our engineering group has developed an oxygen sensor to be used in a leading oxygen concentrator product. Electrical and mechanical engineering challenges included the need to count ultrasonic pulses over very short times and creating a configuration that allows laminar flow over the emitting and detecting sensors. The sensor measures the time-of-flight of an ultrasonic pulse passing through a short section of tubing exposed to concentrated flowing oxygen. This sensor approach was chosen from several methods considered by prototyping and testing.Electrical engineering tasks included the design of the filtering and software to accurately count pulses over very short times. Mechanical design included an injection molded manifold compatible for solvent bonding with tubing designed to allow laminar flow over the emitting and detecting sensors. We acted as manufacturing liaison by setting up a separate company to produce the sensors for our client.