Below are some of the more frequently asked
questions by our customers. If you do not find the
answer you are looking for below, please
contact us and
we will be glad to assist you.
The chart in the
PDF file referenced below illustrates the
outstanding sensitivity of the NORCROSS falling
piston viscometer. This sensitivity, which only the
NORCROSS process viscometer can produce, combined
with the simplicity
and ruggedness of all the falling piston principle.,
create a versatile and long lasting viscosity
sensor/system.
For complete product information,
click
here to download an Adobe
Acrobat PDF file.
Figure 1 shows the two surfaces
with a fluid between them. A force is applied to the
top surface and thus it moves at a certain velocity.
The ratio of the Shear Stress / Shear Rate will be
the viscosity.
Note that as the force is doubled then the velocity
doubles. This is indicative of a Newtonian fluid,
such as motor oil.
Fig 107-1-154
Figure 2 shows what happens when
measuring a Non-Newtonian fluid, such as an ink or
coating. The change in velocity is non-linear.
Fig 107-2-155
Figure 3 shows what happens when
the force is increased even more. Note that while
the force was doubled in each case the increase in
speed is not the same in Figures 2 and 3.
Process viscometers apply more force than efflux
cups and thus will measure this non-linear response.
It is for this reason that when process viscometers
are to display viscosity, as efflux cup seconds,
they need to be calibrated to the specific efflux
cup and process fluid being measured.
Once calibrated they will track changes in viscosity
and can display viscosity in efflux cup seconds.
Fig 107-3-156
Figure 4 shows how the NORCROSS
Falling Piston is a very close approximation to the
basic method of measuring viscosity. This is one
reason the NORCROSS Viscometer is so successful.
Fig 107-4-157
For a full
explanation,
click
here to download an Adobe
Acrobat PDF file.
The basic
measurement unit of viscosity is centipoise. Most
methods of measuring viscosity depend on a direct
relationship to centipoise units for their validity.
For complete product information,
click
here to download an Adobe
Acrobat PDF file.
