Vaisala MM70 User Manual download pdf (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.

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Vaisala MM70 User Manual Page 57