1. Potentiometric measuring principles ABL800 FLEX Reference Manual
pH electrode, Continued
Designation
(continued)
pH(Cal1,nom)
= Nominal pH of Cal 1 solution (pH = 7.4)
pH(Cal1)
= pH of Cal 1 solution
E(pH,Cal1prev) = Potential of the pH electrode chain from the previous
calibration measurement on Cal 1 solution
Sens(pH,prev)
fraction
= Sensitivity of the pH electrode from the previous 2-point
calibration
pH(Cal1,prev)
= pH of Cal 1 solution in the previous calibration
measurement
pH(Cal2)
= pH of Cal 2 solution
Sens(pH)
= Relative sensitivity of the pH electrode chain.
Sensitivity
The sensitivity of the pH electrode (Sens
pH
) is obtained from the calibration line
obtained from a 2-point calibration on Calibration Solutions 1 and 2 (Cal 1 and Cal
2), and is calculated from the following equation:
[]
pH(Cal1)pH(Cal2)61.5
Cal1)E(pH,Cal2)E(pH,
Sens(pH)
−×−
= (fraction)
The sensitivity of the pH electrode should fall between 0.92 - 1.03 or 92 -103 %.
Status
The status of the pH electrode is calculated from the following equation:
pH(Cal1)nom)pH(Cal1, 2
61.5-
Cal1)(pH,ECal1)E(pH,
Status(pH)
0
−+
=
The status of the pH electrode should fall between a pH of 6.7 and 8.1.
Drift
Drift 1 is calculated from the following equation:
[]
prev)pH(Cal1,pH(Cal1)
prev)Sens(pH,61.5-
Cal1prev)E(pH,Cal1)E(pH,
1(pH)Drift −−
×
=
NOTE: Under normal circumstances, pH(Cal1)−pH(Cal1,prev) = 0. However in
instances where the Cal 1 solution container has been replaced between two
consecutive calibrations, pH(Cal1)−pH(Cal1,prev) ≠ 0.
The default drift tolerances set by Radiometer for Drift 1 are ± 0.020.
Drift 2 is calculated from the following equation:
[]
Drift 2(pH)
E(pH,Cal2) E(pH,Cal1prev)
- 61.5 Sens(pH,prev)
pH(Cal2) pH(Cal1,prev)=
−
×
−−
The default drift tolerances set by Radiometer for Drift 2 are ± 0.020.
Continued on next page
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