Galvanic versus Optical Dissolved Oxygen Debate.  

When optical sensor were first launched many claims were made about the extra accuracy and reliability compared to the older membraned technology. It was said that Optical sensors never needed calibrating and never needed cleaning.

As with many marketing claims there was an element in both statements. Optical methods do use an absolute technique to measure oxygen and even if only a small amount of light enters the water it is still possible to measure DO, this means that a partially fouled sensor will still work. Ultimately of course a completely covered sensor will need cleaning.

Early comparisons were between a non cleaned optical system and a old non-cleaned galvanic or polarographic membrane system. In these cases, an optical system will perform better. A more valid comparison would be between AutoClean galvanic and AutoClean optical systems.

ATi decided to investigate further and installed two dissolved oxygen monitors on an aeration lane at a Uk’s Waste Water Treatment site. Both systems featured the ATi air blast Auto-clean system, the only difference is one used the tried and tested galvanic sensor with a Teflon membrane while the other used the optical DO sensor.

After a lengthy trial both monitors were taken out of the effluent and examined.

The sensors were then taken through an air calibration. The optical sensor calibrated with a 100% slope, pre cal 97% and the galvanic with 73% slope, pre cal 70%.

In summary, if a comparison was made between efficiently, both systems show no major differences in performance however the cost of ownership for optical sensors is around 20 times that of the galvanic system. ATi can supply both technologies so ultimately the choice will be down to the end user.