Info DiveGearExpress o2 sensors

[inquis]

I don't calibrate unless the cell doesn't read close enough to the expected value on O2 (i.e., the ambient pressure). I also check the response to an actual 1.6 bar on the first descent of, say, a weekend trip. A pressure pot is convenient, but there are other ways to evaluate performance above surface ambient.

 

[Dsix36]

I get your logic but I think it's dangerous. All sensors have a rate of decline of mV over time (and this rate is different for each sensor). So if you calibrate now and use the same calibration in 6 months, the constant of all sensor will have changed while your computer will be showing the one from 6 months before. Given that constants normally go down (unless the cell has problems), you will be underestimating your pO2 (which is safe for decompression calculation but not conservative with regards to O2 toxicity). Manufacturers say that sensors can be used in the range 40-62 mV which means that if you are using a sensor calibrated at it's peak of 62 mV when new while you dive it towards the end of its life at 40 mV, you will be underestimating your pO2 by 35%. I.e. if you have a set point of 1.3, your computer reads 1.3 in the loop but you are actually breathing 2.0.

It has worked for you for 2 decades so I do not want to convince you but wanted to share my thoughts on this practice for other divers.

I respectfully disagree. If the cells continue to show .21 in air then the mv have not changed enough to make any difference. Then may indeed become limited over time but with a staggered rotation for replacement it is easy to spot any that are starting to slow low at higher partial pressures. I will calibrate if there is more than .01 difference at startup with air. .20 .21 .20 .20 is fine for me. .19 .20 .21 .20 will be calibrated.