WTW Optical FDO® 700 IQ Sensor

Optical working D.O. sensor for the measuring and control of oxygen concentration in the biological cleaning process of wastewater plants

  • Description
  • Essential resources
  • Technical specifications
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Optical working dissolved oxygen sensor for the measuring and control of dissolved oxygen concentration in the biological cleaning process of wastewater plants, no flow required and H2S insensitive. Digital sensor for connecting to the IQ SENSOR NET.

Features and Benefits

  • No incident flow needed
  • No calibration needed
  • H2S insensitive
  • High accuracy right from the start
  • Maximum stability over a long timespan
  • Minimum maintenance effort

FDO : Fluorescence Dissolved Oxygen Measuring – What exactly does this mean?

The optical principle:

With the optical method a fluorescent dye is stimulated in the membrane of the FDO® 700 IQ by a short wave length lightsource. By falling back into the passive state, long wave light is emitted, which is recorded as a measurement signal. If oxygen contacts the dye by diffusing through the membrane the period of back scattering light is shortened according to the oxygen concentration of the sample. In principle the measurement of the fluorescent signal come back to a highly precise time measurement.

Dissolved oxygen sensors of the first generation had a handful of technical issues to cope with.
Sensor drift through watering impact of the membrane
Wearing of cye layer in the sensor through highly energetic blue light
Sensitivity of sensor towards air bubbles
Through consequent development work the difficulties appearing with the first generation sensors could successfully be eliminated with the second generation models.

Optical DO Sensor Specifications

Digital Sensor
O2 concentration 0 … 20.00 mg/l
(0 … 20.00 ppm)
0.01 mg/l
(0.01 ppm)
O2 saturation 0 … 200.0 %
0.1 %

FDO® 700 IQ SW – Sensor in sea water design (with plastic armouring (POM)):

Digital Sensor
O2 concentration 0 … 20.00 mg/l
(0 … 20.00 ppm)
0.01 mg/l
(0.01 ppm)
O2 saturation 0 … 200.0 %
0.1 %