Chapter 6 ____________________________________________________________ ppm Conversion

CHAPTER 6

PPM CONVERSION

This chapter contains information on conversion models.

MMT330 ppm Conversion for Transformer Oils

Traditionally, moisture in transformer oil is measured by using ppm units. The ppm output shows the average mass concentration of water in oil. MMT330 has an option for ppm output provided that this has been selected when ordering the transmitter. Vaisala has this conversion readily available for mineral transformer oils.

Conversion Model with Average Coefficients

The conversion model of the MMT330 is based on the average water solubility behaviour of transformer oils. The ppm output is calculated as follows:

ppm = aw x 10

(A/(T+273.16)+B) where: aw = Water activity

A,B = Coefficients (average/oil-specific)

T = Temperature (ºC)

Generally, measurements with MMT330 give accuracy better than 10 %

of the reading. If additional accuracy is needed, see section Conversion

Model with Oil-specific Coefficients on page 140.

NOTE The internal calculation in ppm conversion uses a w

also when only %RS output is selected when ordering MMT330.

To convert %RS to a w

, divide the %RS quantity by 100: a w

= (%RS / 100)

VAISALA _______________________________________________________________________ 139