How to monitor (high) oxygen content in gas (air)?

How could I go about monitoring (semi-continuously, say, one measurement per 10 minutes) oxygen content in an oxygen-rich air mix (air with substantial amount of nitrogen removed with a [Zeolite](https://en.wikipedia.org/wiki/Zeolite) filter)?


There are questions ([1](https://chemistry.stackexchange.com/questions/5613/how-to-measure-amount-of-oxygen-or-carbon-oxide-in-air), [2](https://chemistry.stackexchange.com/questions/5544/experiment-to-show-that-air-contains-about-20-oxygen) ) about measuring oxygen content in air, using a candle and checking volume after burning. Them being cumbersome is less of a problem - worse that lighting a candle in 80+% oxygen atmosphere can a be quite... energetic reaction.


Are there any other reactions that can provide oxygen content measurements like that, preferably not involving open flame?


(Neither accuracy nor measurement time are very important, but the measurement should be easy to perform, and repeatable, no large amounts of expensive consumables. Something that could be automatized would be nice.)


