TruGap: Direct Measurement of the Real Gap

TruGap™ allows for accurate monitoring and control of the real gap size of parallel-plate and cone-plate geometries, which increases accuracy and reduces preparation time.


Errors in gap dimensions directly influence the accuracy of measuring results in parallel-plate and cone-plate measurements. Therefore an accurate gap setting is needed in order to measure rheological properties correctly. In rheological tests with significant temperature changes, the gap size increases or decreases due to thermal expansion or shrinkage of the measurement geometry. Usually inmodern rheometers this temperature-related gap dimension change is compensated for by using an automatic gap control (AGC) function. AGC corrects the gap mathematically according to a thermal expansion coefficient, which depends on heating rate and material of the measuring geometry. For highly accurate results, the zero gap position has to be determined at the measuring temperature in order to reduce residual gap correction errors of the AGC. For wide temperature ramps, the expansion coefficient needs to be measured for every test in advance – a time-consuming procedure. If zero gap was set at a different temperature and the expansion coefficient is not exactly calibrated, the instrument sets wrong gap sizes and this leads to a wrong evaluation of rheological properties.

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