Methods and devices for controlling the temperature
The temperature gradient in the test chamber surrounding the sample should be as small as possible. There are different methods and devices available for controlling the temperature:
The Peltier effect is a thermoelectric effect. The junction between two suitable materials that are joined as layers (for example, specific metals or semiconductors) is heated or cooled, depending on the applied voltage and the direction of current. The advantage of this method is that both high heating rates and high cooling rates can be achieved. Added to that, the size of these devices is comparably small and the investment and operating costs are relatively low. The available temperature range is usually between -40 °C and +200 °C. There are two types of systems; one featuring a “passive hood” without temperature control and the other one with a so-called “active hood”, where the temperature can be controlled. With these hoods, the temperature gradient is minimal. In order to achieve precise measuring results, such hoods should be used whenever the measuring temperature differs by more than 10 °C from ambient temperature.
Liquid-bath temperature control
This kind of temperature control often uses water or thermo-oil-controlled thermostats; for example, for measurements that are carried out between -40 °C and +200 °C. The disadvantages are low heating and cooling rates and sometimes inconvenient handling of liquids in the laboratory.
This method is suitable for measurements carried out at high heating rates or at constant high temperature, for example between +30 °C and +400 °C.
Convection heating or cooling
The temperature is controlled by using an inert gas such as nitrogen; for example for tests at temperatures between -150 °C and +600 °C. Special measuring devices and furnaces are available for testing samples such as glass, salt, and metal melts at temperatures of up to 1000 °C, and for geological tests on volcanic rocks such as basalt, even up to 1800 °C.