Temperature Compensation
!
Note: The temperature is compensated automatically
only if an ATC probe is connected.
Temperature has two major effects on the results:
1. Temperature affects buffer pH values.
The values are usually given on the buffer label.
Most technical buffers correspond to the values
listed in the table shown here on the left.
When you perform calibration in the pH mode,
the pH value is adjusted to the current value for the
current temperature.
For example, if the buffer has a pH of 7.00 at 25°C
and the current buffer temperature is 20°C, the
portable meter calibrates the buffer to pH 7.02.
2. Temperature affects electrode efficiency.
The theoretical voltage change per pH unit – the
so-called Nernst factor – is approximately 59.17
mV/
∆
pH at 25°C. This value changes, however,
as the temperature changes. The meter compensates
for this effect by calculating the pH measurements
based on the measured temperatures and the
corresponding Nernst factors (for example,
58.16 mV/
∆
pH at 20°C).
29
Standard Buffers:
pH 4.00 pH 7.00 pH 10.00
0°C
4.005
7.13
10.34
5°C
4.003
7.10
10.26
10°C
4.001
7.07
10.19
15°C
4.002
7.05
10.12
20°C
4.003
7.02
10.06
25°C
4.008
7.00
10.00
30°C
4.010
6.99
9.94
35°C
4.020
6.98
9.90
40°C
4.030
6.97
9.85
50°C
4.061
6.97
9.78