ECDO stands for Electrochemical Dissolved Oxygen Sensor. 60 years ago, Clark’s cell was introduced and WTW was among the first manufacturers to advance this principle for water and wastewater applications.

The electrochemical principle
With the electrochemical method the O2 diffuses through the membrane of the TriOxmatic® sensor. The oxygen is transformed in a chemical reaction by using an electrolyte; thereby a current can be measured. The electrical current correlates to the oxygen concentration. For delivering precise results, the sensor will require the following conditions:

• Flow
• Continuous exchange of electrolytes
• Clean membrane

Patented Technology – 3 electrode system
In contrast to conventional membrane covered oxygen sensors equipped with 2-electrode technology, the TriOxmatic® sensor functions with a potentiostatically driven 3-electrode system. In terms of measuring technology, this means that the measuring system has two silver electrodes and a gold cathode (A). One silver functions as a non-current bearing reference electrode (R). And, the other is the live, counter electrode (G). The reference electrode thus displays significantly improved potential constancy, which in turn leads to considerably improved sensor signal stability and thus higher measuring accuracy.
The 3-electrode technology additionally allows precise monitoring of the electrolyte supply, i.e. the system displays when the electrolyte solution needs to be replaced.

Self-diagnosis system
All parts being relevant for the measurement, such as membranes are automatically monitored by the SensReg (used electrolyte)/SensLeck (leakage in the membrane) system. Any occurring incidents will be shown.

Maintenance-free due to special membrane
The membrane or the membrane cap plays a decisive role in all DO measuring techniques. Fouling or mud covering of the membrane or of the cap will affect the measurement reading. Unlike conventional membranes the teflon membranes used by WTW are highly resistent to fouling. This allows operation without the use of additional cleaning accessories in most cases.

High accuracy
WTW sensors feature extremely low maximum errors of 1% of the measured value (i.e. 0.02 mg/ml at a measured value of 2 mg/ml), regardless of whether measuring in the upper or in the lower range of the instrument.

Stable readings right from the start
All WTW ECDOs provide stable and reproducible readings right from the start:

• No break-in
• No long-term drift
• No zero point drift due WTW‘s patented TriOxmatic® principle.