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IM 12B06J03-02EN-P
6.3 Maintenance of the FU20 sensor
A pH sensor requires routine maintenance to keep the measuring elements clean and
functioning. Depending on the process, different cleaning solutions may be required.
Avoid cleaning the complete sensor with solution. Some cleaning solutions will
damage the model code sticker and connector which are placed on top of the
sensor. Only clean the measuring elements at the bottom side of the sensor.
In most cases cleaning with water, iso-propanol or methanol is sufficient. In other cases,
the measuring elements of the sensor have to be cleaned with specific solutions.
Examples:
1. Deposits of limes, hydroxides or carbonates can be removed by immersing the bottom
part of
the sensor in a solution containing dilute hydrochloric acid (5% is recommended).
Afterwards
rinse the sensor with water.
2. Deposits of oil and fat can be removed with hot water with a detergent. When the results
are unsatisfactory, a mild (carbonate based) abrasive can be used.
3. Protein deposits should be removed with a protein enzymatic solution, for instance a
solution containing 8.5 mL concentrated hydrochloric acid and 10 grams of pepsin in 1
liter of water.
Note: Avoid cleaning with non-polar solvent like tri-chloro ethylene, toluene or hexane.
The non-polar solvents will break up the gel-layer on the pH glass bulb and
requires that the sensor has to be soaked in water for at least 12 hours before it
will function again.
The Teflon diaphragm of the sensor can be regenerated by putting it in hot
(± 70 °C, 158 °F) 3 molar Potassium Chlorine (KCl) solution and letting it cool down to
room temperature. This procedure clears the diaphragm and will soak the diaphragm with
conductive KCl again.
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