Electrode Problems
The most common problems experienced with pH electrodes are:
Oily and solid coatings requiring frequent removal for cleaning.
pH bulb breakage or premature failure as a result of abrasives or solid materials in the solution.
Reference junction fouling or plugging requiring frequent removal for cleaning.
Reference side contamination as a result of interactions between the silver ions in the electrodes and materials in the solution which interact with silver. This result is short electrode life.
These problems can be solved by careful pH electrode selection. For example, Sensorex, a manufacturer of pH and ORP electrodes, has developed a durable and economical pH electrode for today's industry. A flat surface self-cleaning electrode has been designed to solve or minimize the above mentioned difficulties. The flat surface design is used rather than the normal spherical shaped bulb for the following reasons:
In a stirred or flowing solution, the back or downstream side of the usual spherical bulb does not see flow and encourages buildup. With flat design, the material is pushed across the face of the electrode with new material pushing away the old. In most applications, the scrubbing action of the flow across the electrode's flat surface keeps it clean.
Breakage or premature failure from abrasion is also reduced by eliminating the protruding spherical bulb; particles simply sweep the flat surface without hitting the glass sensing surface.
Normal spherical bulb type electrodes tend to have very small reference paths. The flat design utilizes a large surface area porous reference junction which has thousands of paths for reference diffusion and the possibility of all of these paths becoming plugged is quite remote.
The flat surface design incorporates a double junction reference design for maximum protection against reference side contamination which can cause premature failure.