User's Guide ______________________________________________________________________
42 __________________________________________________________________ M210934EN-B
Conversion Model with Average
Coefficients
The conversion model of the MMT162 is based on the average water
solubility behaviour of transformer oils. The ppm-output is calculated as
follows:
10
x
aw
ppm
=
((A/T+273.16)+B)
where
aw = water activity
A,B = coefficients
(average/oil-specific)
T = temperature
(ºC)
Generally, measurements with MMT162 give accuracy better than 10 %
of the reading. If additional accuracy is needed, refer to section
Conversion Model with Oil-specific Coefficients below.
Conversion Model with Oil-specific
Coefficients
For additional accuracy, oil-specific conversion model can be used both
for mineral and silicon based oils. An oil sample has to be sent to Vaisala
for modelling. As a result, the specific coefficients (A and B, see
formula 1) for the transformer oil are determined by Vaisala. For
additional information, please contact Vaisala.
The determined coefficients of the transformer oil can be programmed to
the MMT162 by Vaisala or by a user according to the instructions
presented in this chapter.
NOTE
Conversion model with oil-specific coefficients is always needed for
silicone based oils.
