For centuries people were only able to grasp temperatures subjectively as cold or hot. The invention of the first objective temperature measuring device based on the expansion of air goes back to Galileo Galilei approx. in 1592. Today temperature measurement technique disposes of a great number of highly specialized sensors and methods that allow to determine exactly and reproduce the thermodynamic state of the matter and thus its temperature almost between 0°K and for example the temperature of the sun.
The Fahrenheit scale
The German Gabriel Fahrenheit settled down in the Netherlands as instrument maker and built glass thermometers with mercury filling. In 1714 he divided the temperature range between a so called „cold mixture” (ice and salt) and the temperature of human blood (these were his points of reference) into 96 pieces. Later on it was determined in England that the solidification point of water corresponds to 32°F and its boiling point to 212°F.
Electric thermometers turn the physical value of temperature into a dependent signal. They are self-contained
constructive components that deliver an output signal for further treatment. Dependent on the sensor principle in most
cases an auxiliary energy source is necessary.
An important advantage results out of the good transferability of those electric symbols over far distances. The
transducer and indicator of temperature can be situated far away from each other. The measuring signals can be
integrated and treated with small effort into control respectively process guiding systems.