ABB 7651, Инструкция по эксплуатации

Страница: 17 / 24

15
5 CALIBRATING THE SYSTEM
5.1 General Calibration of Electrodes
When the electrode system has been connected correctly and all
electrical connections made to the associated pH transmitter, the
system is ready for calibration by immersing the electrodes (using
suitably sized beakers) in either:
• A calibration solution (buffer) of known pH value for a single-
point calibration.
or
• Two separate calibration solutions of known pH values for a
two point calibration. For electrode systems in use:
a) Remove the electrode from the process or sample.
b) Wash the visible electrode surface with demineralised water.
Refer to the instruction manual for the pH transmitter for full
details of the calibration procedure.
Note . Do not use 10pH buffer solutions with Low
Resistance Glass pH Electrodes as this results in an
error in the slope calculation. These solutions contain
a high level of sodium that affects the output of the
electrode, due to sodium response interference at
high pH values.
5.2 Calibration of Electrodes used in High Purity
Water Applications
5.2.1 Monthly Calibration
a) Rinse the electrodes thoroughly with high purity water.
b) Carry out a single-point calibration using a 5-fold diluted 9 or
10pH buffer solution, to adjust for small changes in the Check
Reading. If necessary, leave the electrodes in the solution to
fully equilibrate at the buffer solution temperature.
Note . These solutions are contaminated easily so
they must be freshly prepared from the original
solution, used only once and keep solution in a closed
container.
5.2.2 3-Monthly Calibration
a) Rinse the electrodes thoroughly with high purity water.
b) Carry out a two-point calibration using normal strength buffer
solutions. If necessary, leave the electrodes in the solution to
fully equilibrate at the buffer solution temperature.
c) Carry out a single-point calibration as described in the
monthly calibration procedure.