Vaisala MM70 - Manual (Page 57)

Chapter 5 ___________________________________________ CALIBRATION AND ADJUSTMENT
8. Calibration is done. To return to the basic display, first press the
BACK key and then press the EXIT key.
Last Adjustment Date
To see the last adjustment date, select Last adjustment date. You can
check this date also from the Device information. For more
information, see section Device Information on page 29.
Determination of Oil-specific Coefficients
The equation of the Ppm conversion 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
- for example, a conical flask (1L) sealed by PTFE stopper
with an inlet for a moisture probe
- MMT330 by Vaisala
- 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 MMT330 at two
temperatures that differ at least 20 °C. Follow the measurement
stabilization illustrated by the graph.
NOTE The sample has to be sealed very carefully i.e. not to be in contact
with ambient air, which would change the water content.
VAISALA _______________________________________________________________________ 55