Materials Science
Advancements in Instrumentation for Viscosity Measurements
T
he electronics revolution within the in- strumentation industry has continued at an extraordinary pace, as can be seen with the many recent improvements in display technology and “smart” operating features. These advances have been especially remark- able in the latest generation of devices for measuring viscosity and yield stress. User in- terface now includes touch-activated screens that easily access built-in libraries of reference information on test methods. Accessory items for use with the instrument, like temperature baths, can be monitored directly. Controlled user access and data security, which are re- quired to comply with standards such as 21 CFR Part 11 in the U.S. Federal Register, are be- coming normal features in today’s viscometers and rheometers. Simple and complex tests alike can execute automatically without direct operator involvement to monitor data output.
So much new capability has been incorporated into today’s instruments that the laboratory benchtop now has a host of time-saving and error-reduction opportunities that cannot be overlooked. “Why?” you ask. “What could pos- sibly justify such an investment at this time?” Two answers jump right out. First, productivity gains are measurable and significant. Second, no more operator mistakes occur because the viscometer or rheometer is in control. Does this mean a reduction in force for lab staff? No, lab techs now have time to address growing sample volume throughput and the addition of extra tests for yield stress. In the case of materi- als like adhesives and pastry icings that need to hold their shape, creep behavior can also be assessed. So the bottom line is a clear return on investment that guarantees payback within the first year of operation.
New rheometers, like the instrument shown in Figure 1, represent the most advanced capabil- ity in the worldwide market for viscosity and yield stress measurement. Ease of use is fa- cilitated by new touchscreen interfaces, which
by Robert G. McGregor
Figure 1 – Brookfield DV3T Rheometer with touchscreen interface (Brookfield Engineering Laboratories, Middleboro, MA).
have become the standard due to the market proliferation of everyday handheld devices, such as smartphones, tablets, etc. Lab techni- cians can quickly access specific viscosity and yield stress test methods stored in memory in the standalone instrument. Connection to a computer was necessary in the past, but this is negated by the built-in computer within the instrument itself. Both R&D and QC benefit, because the work of R&D to create the test methods automatically transfers to QC once the methods are stored in the instrument.
Viscosity test data can now appear live on the screen in graphical format with the added benefit of showing trend behavior. The data on the screen, as shown in Figure 2, permit visual acceptance or rejection at a glance. The instrument by itself can actively monitor the measured viscosity and yield stress values and report whether the data fall between allowable QC limits established by the user. These windows for data acceptability are pro- grammed into the instrument by the user and automatically show whether the test passes or fails. Interpretation of results therefore be- comes automatic and provides the operator more time for other responsibilities.
These improvements help to increase both the quantity and quality of data generated per test.
AMERICAN LABORATORY • 18 • SEPTEMBER 2013
Figure 2 – The graphical data output on the rheometer screen characterizes material flow behavior at a glance.
They also streamline the test in terms of the time required to execute. Since the market price for these types of instruments is typically under $5000, R&D can easily afford the purchase to do the initial method development. Then there is added assurance that QC can also afford the same unit due to its relatively low cost, making it a double win for both departments.
New capabilities in viscosity testing Touchscreen interface to visually observe
viscosity test data Below are some examples of the change in test methodology that becomes possible using
Figure 3 – Temperature bath controlled by a Brookfield DV2T viscometer.
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