Vaisala HUMICAP MMT310 Podręcznik Użytkownika Pobierz pdf (Strona 59)

Appendix 1 _____________________________________________________________ Applications

VAISALA _______________________________________________________________________ 57

Calculation Model with Average Coefficients

The calculation model of the MMT318 and MMT317 is based on

the average water solubility behaviour of transformer oils. The

ppm-output is calculated as follows:

= awppm

(A/(T+273.16)+B)

(1)

Where aw= water activity

A,B= coefficients (average/oil specific)

T= temperature (ºC)

Generally, measurements with MMT318 and MMT317 give accuracy

better than 10 % of the reading. If additional accuracy is needed, refer

to the paragraph Calculation Model with Oil Specific Coefficients.

Calculation Model with Oil Specific Coefficients

For additional accuracy, oil specific calculation 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.

Using these coefficients the accuracy of measurements is increased.

The determined coefficients of the transformer oil can be programmed

to the MMT318 and MMT317 by Vaisala or by a user according to

the instructions presented on page 58 .

NOTE

Calculation Model With Oil Specific Coefficients is always needed

for

silicone based oils.

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Vaisala HUMICAP MMT310 Podręcznik Użytkownika Strona 59