I'm using an optical dissolved oxygen sensor, in which oxygen concentration is measured using the fluorescence of a dye in the sensor (see page 9 of https://www.fondriest.com/pdf/ysi_do_handbook.pdf). The lifespan of the sensor is determined by "degradation of the dye over time" - but I want to know if this is time per se or depends on the number of measurements. Does each measurement degrade the dye? Will the dye last for n days or n readings, or some combination of the two?