The ongoing debate in waste water of “optical or galvanic?” for dissolved oxygen measurement is becoming more interesting. End users from within the water industry are starting to see that the real issue is not the sensing technology it is the cleaning.
To recap, we started the trial over 24 months ago on an aeration lane at a waste water treatment site in the UK. Both installations included the ATi air blast AutoClean technology. One unit featured a galvanic sensor with Teflon membrane and the other used an optical sensor.
There has been no manual intervention with both sensors. A calibration check after 2 years showed that the optical sensor calibrated with 100% slope (pre cal 97% slope) and the galvanic sensor calibrated at 73% slope (pre cal 70%). Both sensors are still clean and in good working order.
The only difference between both auto-clean sensors, seems to be the long term cost of ownership? We totally agree that the galvanic sensor without auto-clean won’t work as accurately as the optical, but all waste water applications will require sensor cleaning. We supply both systems and always recommend the auto-clean; a dirty sensor will either read low or not at all whatever the technology.
Ultimately the decision is up to the end user; at present our trial shows that the auto-clean optical sensor is no better than the tried and tested membrane technology, just more expensive to own and buy.