Vaisala HMP228 Guía de usuario descargar pdf (Pagina 21)

Chapter 7 ___________________________________________________________________ Settings

VAISALA _______________________________________________________________________ 19

CHAPTER 7

SETTINGS

PPM-calculation

In case you have a device with a ppm-output the ppm-value is available as

one of the quantities. The calculation model is based on the average water

solubility behaviour of transformer oils, as follows:

10×= awppm

(A/(T+273.16)+B)

Where aw= water activity

A,B= coefficients (average/oil specific)

T= temperature (ºC)

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) for

the transformer oil are determined by Vaisala. Using these coefficients the

accuracy of measurements is increased. The determination of specific

coefficients shall be agreed with the Vaisala representative.

The determined coefficients of the transformer oil can be programmed to

the MM70 by Vaisala or by a user according to the following instructions.

NOTE

Calculation Model With Oil Specific Coefficients is always needed

for silicone based oils.

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Vaisala HMP228 Guía de usuario Pagina 21