Vaisala MMT162 - Manual (Page 47)

Chapter 4 ________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 45
Determination of Oil-Specific
Coefficients
The equation of the ppm calculation is:
ppm = aw×10 (B+A/T)
With the following procedure the coefficients A and B can be defined for
the equation:
LOG(PPM
sat
)= B + A/T
Equipment needed:
- Apparatus for determining water content ( for example, coulometric
titrator and e.g. magnetic stirrer.)
- Oil test station:
- a temperature test chamber.
- a suitable container (for example, a conical 1 L flask) sealed
by PTFE stopper with an inlet for a moisture probe.
- a MMT162 transmitter by Vaisala.
- a magnetic stirrer.
Procedure:
1. Define the water content of the oil sample with the titration. Use
the oil moisture level that is close to real conditions in the process.
2. Measure the water activity of this sample with MMT162 at two
temperatures that differ at least 20 °C.
NOTE The sample has to be sealed very carefully. Contact with ambient air
will change the water content.
NOTE If the oil sample is very dry and the temperatures are close to each
other, it may cause inaccuracy to the calculation model. In order to
get the best possible performance it is recommended to use oil
conditions that represent real conditions in application.
Recommended values for sample are aw approx. 0.5 at 20 °C.