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ViSmart Theory of
Operation
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The industry is familiar with kinematic viscosity (centistokes)
and dynamic or absolute viscosity (centipoise), which are
related as centistokes = centipoise / specific gravity. BiODE’s
instrument introduces a third class of viscosity called acoustic
viscosity.
Acoustic viscosity has units of centipoise X specific gravity.
Knowledge of the specific gravity allows conversion between
these three units at a fixed shear rate and temperature. This
method of measuring viscosity employs a shear acoustic wave
resonator in contact with the liquid. |
ViSmart™ Sensor |
The
viscosity of the liquid determines how thick a layer of fluid is
hydro-dynamically coupled to the surface.
The loading of the
acoustic resonator caused by this viscously-entrained liquid is
determined by the thickness and density of the entrained film. The
response of an acoustic viscometer is thus proportional to the product
of the viscosity, the density and the radian frequency of the vibration
in the limit of low frequencies.
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The acoustic wave
resonator supports a standing wave through its thickness that travels
from the input to the output transducer. As the wave pattern interacts
with electrodes on the lower surface (sealed from the liquid) it also
interacts with the fluid on the upper surface. The bulk of the liquid is
unaffected by the acoustic signal and a thin layer (on the order of
microns or microinches) is moved by the vibrating surface (the vibration
amplitudes are on the order of a single atomic spacing). As the
vibrating surface moves the thin layer the characteristics of the
acoustic signal changes; these changes are related to the viscosity of
the fluid. |
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Historically, for real-time viscosity data, costly and inflexible
mechanical products have been used. Up until now there has been no
viable “electronic way” to measure viscosity and processors have been
forced to measure infrequently or utilize a wide range of methodologies
with repeated cost/benefit trade-off. For process engineers, there is a
need for minimizing equipment failures and reducing the cost of analysis
using an oil viscosity sensor that operates in real time.
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ViSmart™
acoustic wave,
resonance based electronic viscosity sensor and measurement systems
changes all this and provides a solution oriented product to the oil
condition monitoring industry. |
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