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[August 2001]
Direct Strain Control Oscillation
Bohlin Instruments Ltd (Cirencester, England) has developed a direct strain control oscillation feature for its digital DSP based rheometer range, which includes the new C-VOR. The new oscillation mode enables oscillation tests to be performed directly at a pre-set strain amplitude.
This feature, says the company, can be especially useful in a number of practical applications. For example, it avoids the time consuming need to iteratively adjust the stress amplitude on successive oscillation cycles in order to achieve a target strain. For curing or gelling systems where rapid changes in modulus can lead to large variations in strain if a stress controlled test is performed, it is now possible to directly regulate the strain amplitude.
This not only generates data points more rapidly, points out Bohlin, but also has the additional benefit of closely controlling the sample's strain history. In addition to the strain controlled oscillation testing, the company has also introduced partial wave analysis for the oscillation mode. This feature dispenses with the need to sample an entire waveform during an oscillation test. Instead, the user can select just part of a wave to be analysed with, typically, just a minimal loss of precision in modulus or phase angle resolution.
Besides obvious time saving advantages for general work, the partial wave mode is able to give extremely fine resolution along with the time domain during material transitions such as curing where, for example, several points per second can be acquired at 1Hz oscillation frequency.
Web site: http://www.bohlin.com/
ENDS