Aufbau eines hochgenauen Laborthermostaten

The aim of this work was the development of a laboratory thermostat for the highly
precise temperature control. The fluctuation of the temperature should be less than a
millikelvin. The thermostat was designed to control the temperature of various measuring
devices. To achieve this, the parameters of the controller had to be ajusted to
different properties of the controlled system, such as various dead-times or delay-times.
For this purpose, different empirical methods were tested. Further it was tried to optimise
the parameters in a more theoretical way. This was attempted by using the simulation
program Scilab and the mathematics program Mathematica. With the aid of those
programs, a model could be developed wich allows e.g. to investigate reactions of the
thermostat to changes in the nominal value of the temperature or external disturbances.
The Cotton-Mouton-Effekt is very sensitive to changes in temperature near the
isotropic- nematic phase-transition of a liquid crystal. So it can be used to test the
performance of a thermostat.With an equipment for the measurement of the Cotton-
Mouton effect a series of measurements was accomplished over a larger temperature
range. It could be shown that it was possible to get closer to the phase transition, than it
was possible with commercial thermostats.