Interpretation of the measurement results
HySense
®
CX 197
44
ENG
Slow increase
This indicates (as for viscosity) an oil aging that can have various causes:
•
Oxidation (see point 6.1.1 viscosity)
•
Reduction of additives:
Due to the usually polar reduction or decomposition products, the
permittivity increases
•
Humidity increase:
Since water has a very high permittivity (dipolar property), the permittivity
increases with increasing water content. Here, the measurement value
“relative humidity” provides insight.
Quick increase/decrease
If there is a jump in the permittivity, it has to be assumed that there has been a
recent event. In addition to sudden wear (e.g. due to contamination, water, etc.),
there may also have been an oil top-up or oil change.
A frequent error is due to the confusion of mineral and “biological” fluids. Here
you can see the differences in permittivity clearly. The variable range of
poly(alcyl)glycols (>5) deviates significantly from other oils.
6.1.3 Conductivity
Oils are not conductive and have a very small conductivity value of few nS/m.
Since the measurement variable is so heavily dependent on temperature that it
can change by a multiple across the temperature, there is no temperature-
compensated conversion.
Instead, the conductivity is regarded sooner as an indication in order to
determine larger changes in the oil property. A change of the conductivity
generally also causes a change in the permittivity.
The following causes can cause a change in the conductivity:
•
Acids and bases (ion conductivity)
•
Heavy contamination with conductive particles
•
Water ingress
Note
When comparing the measurement value for conductivity, heed the same
temperature.