TA AR-G2, Getting Started Manual

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AR-G2/AR 2000ex/AR 1500ex Getting Started Guide Page 27
Normal Force Transducer (AR-G2 and AR 2000ex Only)
Normal force is detected on the static lower measuring geometry assembly using high sensitivity load cell
technology. This results in a fast response, wide range signal, which is easy to calibrate, and has a genuine
normal force measurement capability.
Both the AR-G2 and AR 2000ex rheometers have the ability to control the amount of normal force during
an experiment, and make quantitative measurements of normal forces generated by a sample during a test.
CAUTION: During sample loading and measurement, the normal force transducer is protected
from overload. However, take care when cleaning or attaching accessories to the lower plate that
you do not exceed the maximum normal force.
When a viscoelastic liquid is sheared, a force can be generated along the axis of rotation of a cone or paral-
lel plate geometry. For this to happen, the structure responsible for the elasticity must not be completely
disrupted by steady shear.
For this reason, colloids, suspensions, etc., although elastic at rest, become effectively inelastic under
steady shear and can show negative normal forces due to inertial effects. However, polymer solutions and
melts, and products incorporating them, are typically elastic under shear because of the long lifetime of the
molecular entanglements.
Normal force measurements are made with cone and plate or parallel plate geometries; therefore, it is
important to use a method to detect the force that does not allow significant changes in the gap. This would
result in the actual shear rate varying with normal force, due to deflections of the force-detecting compo-
nent.
Front Panel
Some of the operation of the rheometers can be controlled through buttons on the front panel, as shown in
the figure, as well as through the rheometer software.
Figure 7 Front panel.
On/Off
indicator
Head
up
Head
down
Stop
Start
Bearing
lock
Zero
gap
Release