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< 3. Maintenance on operation >
3-2
IM 12B7J2-01E
3.2 Operation and Periodic Maintenance
3.2.1 Calibrating pH Sensor Using Buffer Solutions
Calibrate pH sensor with buffer solutions before starting normal operation because the emf of glass
electrodes differs somewhat from each other.
The emf of a glass electrode gradually changes due to electrode staining or deterioration.
Therefore, buffer solution calibration must be carried out periodically within a given period of time to
keep the measurement errors within the limits specified.
For more detailed information on the calibration procedures, see relevant pH transmitter/converter IMs.
3.2.2 Replenishment of KCl Solution
When the KCl solution in the tank seems to be nearly exhausted while using a pH sensor with general
type reserve tank, replace the reserve tank with new one (provided separately as spare part).
Instead of tank replacement, when a KCl solution prepared using KCl powder is used for
replenishment, use 3.3 mol/Lsolution by dissolving 246 g of KCl powder in pure water to make exactly
one liter of solution. When pouring the solution into the tank, be careful that KCl solution does not
overflow from the vent holes of the tank.
3.2.3 Cleaning Glass Electrode and Liquid Junction
Staining of a glass electrode or liquid junction can cause measurement errors. Therefore, if its
measured solutions tend to stain the electrode, the glass electrode and liquid junction must be
cleaned periodically — the period depending on the degree of staining.
Submerge the glass electrode in a diluted hydrochlonic acid solution (1 to 2 %) for several minutes.
3.3 Replacing Consumable Parts
3.3.1 Replacing Glass Electrode
If buffer solution calibration becomes impossible due to deterioration of the glass electrode, replace it
with a new one. After the glass electrode is replaced, always carry out a buffer solution calibration.
3.3.2 Replacing Liquid Junction
Even after washing the liquid junction, if normal measurement cannot be made, replace the liquid junction.
When replacing the liquid junction, fill the sensor with KCl solution to just before the solution overflows
through the liquid junction mounting hole. Use a 3.3 mol/l KCl solution (a higher concentration of KCl
or KCl powder) for this application.
1. When the liquid junction
is to be removed.
2. When the liquid junction
is to be installed.
F3.3.ai Figure 3.2 Replacing Liquid Junction
11th Edition : Nov.20,2018-00