Vaisala HUMICAP MMT162 Guide de l'utilisateur télécharger pdf (Page 51)

Chapter 4 _________________________________________________________________ Operation

VAISALA ________________________________________________________________________ 49

3. Define the correlation between aw, T and PPM (w/w) from the

measured values. Calculate A and B according to the following

example.

[ ]

( ) ( )

-2

PPM

LOGT

PPMLOG

sat

))

[ ]

)(

A/T1

1TPPMLOGB

sat

Example (measured water content 213 ppm):

T (°C)

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.

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Vaisala HUMICAP MMT162 Guide de l'utilisateur Page 51