Hanna-instruments HI 9124 Instrukcja Użytkownika Pobierz pdf (Strona 18)

Typical Electrode Life

Ambient Temperature 1 – 3 years

90 °C Less than 4 months

120 °C Less than 1 month

Alkaline Error

High concentrations of sodium ions interfere with readings in alkaline

solutions. The pH at which the interference starts to be significant

depends upon the composition of the glass. This interference is called

alkaline error and causes the pH to be underestimated. Hanna’s glass

formulations have the indicated characteristics.

1.0 Mol L

-1

0.1 Mol L

-1

Sodium Ion Correction for Glass at 20-25

Concentration pH Error

13.00

13.50

14.00

12.50

13.00

13.50

14.00

0.10

0.14

0.20

0.10

0.18

0.29

0.40

The resistance of glass electrodes partially depends on temperature. The

lower the temperature, the higher the resistance. It takes more time for

the reading to stabilize if the resistance is higher. In addition, the response

time will suffer to a greater degree at temperatures below 25 °C.

Since the resistance of the pH electrode is in the range of 50 – 200

Mohms, the current across the membrane is in the pico Ampere range.

Large currents can disturb the calibration of the electrode for many

hours.

For these reasons high humidity environments, short circuits and static

discharges can be detrimental to a stable pH reading.

The pH electrode’s life also depends on the temperature. If constantly

used at high temperatures, the electrode life is drastically reduced.

TEMPERATURE CORRELATIONTEMPERATURE CORRELATION

TEMPERATURE CORRELATION

FOR FOR

FOR

H SENSITIVE GLASSH SENSITIVE GLASS

H SENSITIVE GLASS

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 27 28

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