Rheometer for polymer [capillary rheometer] Isobaric PVT Measurement according to ISO 17744

What is isobaric PVT measurement? And what is the difference in between isothermal and isobaric PVT measurement?
It is very common to perform isothermal PVT measurement.
PVT isothermal
During isothermal PVT measurement, the temperature is kept constant, while the volume is measured as a function of different pressures. The material is filled at melt temperature and then slowly cooled down under pressure to the 1st measuring temperature. After stable temperature conditions are reached, the different pressure levels are set and the respective volumes are measured and recorded. This process is repeated for each temperature step.
Meanwhile Isobaric PVT measurement is unique as it gives better result compare to isothermal PVT measurement.
PVT isobaric
During isobaric PVT measurements, the volume is determined at constant pressure as a function of temperature. The material is filled in at melting temperature and heated up to the starting temperature. Then a constant pressure is applied. Cooling is started and controlled to a constant cooling rate. During cooling, the volume is recorded as a function of the temperature. Afterwards, the system heats up again fully automatically and sets the next pressure level. In this way, any number of isobars at different pressures can be measured fully automatically with a single barrel filling.
Video credit: Goettfert Gmbh
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