Thermometer User Manual

TEMPERATURE CORRELATIONTEMPERATURE CORRELATION

TEMPERATURE CORRELATION

FOR FOR

FOR

H SENSITIVE GLASSH SENSITIVE GLASS

H SENSITIVE GLASS

Typical Electrode Life

Ambient Temperature 1 – 3 years

90 ºC (194 ºF) Less than 4 months

120 ºC (248 ºF) 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 the Glass at 20-25 ºC (68-77 ºF)

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 the 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 ºC (77 ºF).

Since the resistance of the pH electrode is in the range of 50 – 200 Mohm, 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 are 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.