ATI
Q46D-ODO Optical D.O. System
Part 3 – Optical Sensor Mounting
14
O&M Manual
Rev-J (8/17)
3.2 Optical Sensing
Optical D.O. measurement employs a technique called “fluorescence quenching”
in order to measure molecular oxygen. The sensor will respond to oxygen either
in the air or dissolved in water.
A polymer element at the end of the sensor contains an embedded fluorescent
dye. When the element is exposed to a pulse of light from an internal LED, the
material in the polymer will fluoresce, or emit light at another wavelength. This
light decreases (or is quenched) at a rate proportional to the amount of oxygen in
the polymer. The monitor measures the rate at which this quenching occurs and
calculates the oxygen concentration based on the measurement.
Optical oxygen sensors provide the ability to measure oxygen in stagnant water,
and are not affected by certain kinds of non-biological coatings. However, optical
sensors are affected by biologically active coatings and must be kept clean. In
activated sludge applications, biological films can have a much lower D.O.
concentration on the sensor side of the film than on the bulk solution side. The
automatic air cleaning system integrated into the Q46D system will eliminate
coating problems by cleaning the sensor on a regular programmed schedule.
Figure 7 - Optical Sensor Element
