TRUE GAP CONTROL: DIRECT MEASUREMENT OF THE REAL GAP SIZE DURING PARALLEL-PLATE AND CONE-AND-PLATE RHEOLOGICAL EXPERIMENTS
The actual size of the measuring gap in rotational rheometers has been a matter of discussions for a long time. An error in the gap size influences directly the measuring results in parallel-plate and cone-and-plate measurements. In modern rheometer the length change of the measurement systems due to thermal expansion is taken into account by using gap correction routines. However, these adjustments are based on fixed expansion coefficients, which do not describe transient behavior during temperature ramps and due to changing laboratory conditions. In order to overcome the limitations of existing gap adjustment procedures Physica TruGapTM (US Patent 6,499,336) was developed, which directly measures the actual gap size during the running experiment. The measuring principle is based on an induction method. Since it does not require any mechanical interaction with the sample the rheological experiment will not be influenced by the gap measurement at all. The described Physica TruGapTM device is working over an extended temperature range and can be incorporated into Peltier, electrical resistance, and convection based environmental systems, respectively
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