NAVI F-52, Инструкция по эксплуатации

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Chapter 16 Reference
16.1 pH measurement
F-52, 53, 54, 55 217
●
Temperature conversion
Difference between temperature compensation and temperature conversion
When measuring pH with the electrode, the electromotive force of the glass electrode per 1
pH changes depending on the temperature. Electrical compensation of this change is defined
as the temperature compensation. Therefore, the pH meter to which only the temperature
compensation is given can obtain the pH value at the measured temperature.
Potential difference (Electromotive force) per 1 pH <JIS Z8802-1978>
PH temperature conversion of sample
pH value of a sample changes depending on the temperature and the degree in this change dif-
fers depending on the temperature characteristic of each sample. Therefore, the pH electromo-
tive force changes according to the change in temperature and this change in the
electromotive force becomes an input to the pH meter. Then, it is called the temperature con-
version to correct the change in pH value by this temperature change and convert it to the pH
value at the conversion temperature.
pHx:
PH value at x
℃
after conversion
pHt:
PH value at t
℃
α
:
Temperature conversion factor
[pH/
℃
]
t:
Temperature of sample
x:
Conversion temperature
Hence, the temperature coefficient of the sample is obtained by the following equation.
Note that the error tends to occur when pH-temperature characteristics of the sample is not
linear or when the temperature coefficient is not constant (i.e. pH value changes even in the
same temperature).
Temp.
℃
2.3026RT/F mV Temp.
℃
2.3026RT/F mV
0 54.20 35 61.15
5 55.19 40 62.14
10 56.19 45 63.13
15 57.18 50 64.12
20 58.17 55 65.11
25 59.16 60 66.11
30 60.15 65 67.10
pH
x
pH
t
a t x
–
( )
–
=
a
pH
t
pH
x
–
( )
t x
–
( )
---------------------------- =
[pH/
℃
]