Vaisala MMT310 User Manual
Page 14
User's Guide _______________________________________________________________________
14 ___________________________________________________________________ M210474EN-C
Vaisala HUMICAP
moisture in oil transmitters MMT318 and MMT317
are designed for industrial applications. They measure water in oil in
terms of water activity (aw) which can be determined as follows: water
activity indicates the amount of oil in the scale of 0 - 1 aw. In this scale, 0
aw is an indication of completely water free oil and 1 aw an indication of
oil fully saturated with water. Water is present in free form. The water
activity is used for alarming at the point of > 0.9 aw where the risk for
free water is obvious.
The most advanced feature which distinguishes the measurement of
water activity (aw) from the traditional measurement of absolute water
content (in ppm) is that in the water activity measurement the saturation
point remains stable regardless of the oil type, aging of oil or additives
used. As water activity of the oil exceeds 0.9 aw, there is a risk for
segregation (especially if the temperature decreases).
The MMT318 and MMT317 transmitters can be used for continuous on-
line measurements and can be calibrated against salt solutions, no
reference oils are needed.
Appendix A on page 75 presents application information when using the
MMT318 and MMT317 with transformer oil (output unit= ppm). General
information on paper machine use is also included in the Appendix.