Vaisala MMT330 - Manual (Page 141)

Chapter 6 ____________________________________________________________ ppm Conversion
VAISALA _______________________________________________________________________ 139
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. Vaisala has this conversion readily available for mineral transformer
oils.
The moisture and temperature transmitter MMT330 has an option for
ppm-output provided that this has been notified as placing the order of
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:
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 MMT330 give accuracy better than 10 %
of the reading. If additional accuracy is needed, refer to the paragraph
Conversion Model with Oil-specific Coefficients below.