Digitally controlled high-precision thermostat for X-ray investigations onlyotropic and thermotropic liquid crystals

The construction of a special hot air generation system for X-ray diffracti on investigations of lyotropic and thermotropic mesophases at different tem peratures is described. The sample is positioned at the center of the X-ray diffractometer contained in a long cylindrical capillary, and resides at a small goniometer head used to adjust the precise position and inclination of the sample. It was decided to use air as the medium and initially the me dium was intended to flow axially. A stream of air is blown from a small an d high rectangular opening sideways toward the sample. The gas streaming ou t of the vessel has to pass through a vortex cell. The air leaving the vort ex cell forms a core of whirling gas with constant temperature. A temperatu re sensor is mounted longitudinally above the sample and is positioned insi de the same airflow core. The sensor provides the input signal for a microp rocessor-based controller which regulates the power of the heating or cooli ng system in the inlet tube providing constant temperature in the gas core.