Yokogawa SC25F - Manual (Page 18)

IM 12B6J1-41E-E
18
6.2 Maintenance of the SC25F 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 modelcode sticker and connector which are placed on the electronic
housing 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 Chloride (KCl) solution and letting it cool down to room temperature. This
procedure clears the diaphragm and will soak the diaphragm with conductive KCl again.