Brookfield DV3T Rheometer - Manual (Page 31)

Brookfield Engineering Labs., Inc. Page 31 Manual No. M13-2100
Figure III-7
Initiate temperature control by pressing the Test Connection. The connection status will be confirmed
with a message box and the appearance of the bath icon in the status bar (see Section II.3).
The Default Temperature is the temperature value that the control device will return to at the
conclusion of a Test. This value is set only if the check box is checked. When the check box is
unchecked, the temperature controller will hold at the last set point used in the Test.
TIP: When a test involves several temperature set points, set the Default Temperature to the first
set point used in the Test. This will reduce the transition time from one Test run to the next
Test run.
III.6 Multiple Data Points
The majority of viscosity and yield stress measurements are made at the quality control level and
often consist of a single data point. The test is conducted with one spindle at one speed. The data
point is a useful bench mark for the go/no-go decision in a production setting. The DV3T can be
used for single point measurement.
Many fluids exhibit a characteristic change in viscosity and yield stress with a change in applied
force. This non-Newtonian flow behavior is commonly seen in paints, coatings and food products
as a decrease in viscosity as shear rate increases or an increase in yield stress as a rotational speed
increases. This behavior cannot be detected or evaluated with the single point measurement.
Non-Newtonian flow is analyzed through the collection of viscosity data over a range of shear rates
and the generation of a graph of viscosity versus shear rate (a rheogram). This information will
allow for a more complete characterization of a fluid and may help in formulation and production
of a product. The DV3T is capable of collecting multiple data points for comprehensive analysis
of flow behavior.
More information on flow behavior, shear rate and rheograms is available in our publication, “More
Solutions to Sticky Problems”.