Vaisala MMT162 - Manual (Page 48)

User's Guide ______________________________________________________________________
46 __________________________________________________________________ M210934EN-C
3. Define the correlation between aw, T and PPM (w/w) from the
measured values. Calculate A and B according to the following
example.
[ ] [ ]
( ) ( )
1 / 1 - 2 / 1
1 ( - 2 (
T T
T PPM LOG T PPM LOG
A sat sat
) )
=
[ ] ) (
A/T1 - 1 T PPM LOG B
sat
=
Example (measured water content 213 ppm):
T (°C) aw ppm
saturation
24.1 0.478 213/0.478 = 445.6067
57.6 0.188 213/0.188 = 1132.979
A = (LOG(1132.98)-LOG(445.607))/(1/(57.6+273.16)-
1/(24.1+273.16)) = -1189.4581
B= LOG(445.607)-(-1189.4581)/(24.1 + 273.16) = 6.6503583
Assumptions:
The isoterm of water activity versus water concentration is linear and the
solubility curve has the form of the given equation.