Hach-Lange ORBISPHERE 31xxx Installation and Maintenance - Manual (Page 35)

33
Maintenance
5.4 Hydrogen sensor cell cleaning
Conditions
The hydrogen analyzer works on the principle that hydrogen molecules, passing through the
membrane, generate an electric current at the platinum anode surface. For this to take place, an
extremely clean metal surface is essential. If any film, grease or other impurity covers the
platinum surface, the reaction is impeded and may even be stopped.
In addition, the chemical reaction that takes place on the chloridized silver cathode leads to loss
of performance after a certain operation time.
As a result, a sensor service must be carried out to restore its original performance.
Method
The procedure for cleaning the H
2
electrochemical sensor requires the use of the
ORBISPHERE 32301 Sensor Cleaning and Regeneration Center. This procedure is explained
in detail in the 32301 Operator's Manual.
As an overview, H
2
electrochemical sensor cleaning consists of the following sequence of
operations:
• Dechloridization of the cathode: This process removes the chloride film from the silver
cathode surface (carried out by the ORBISPHERE 32301).
• Rechloridization of the cathode: A layer of silver chloride is grown on the cathode's surface
(carried out by the ORBISPHERE 32301).
• Activation of the platinum anode: The center anode surface is polished, and treated with
nitric acid.