2. Errors due to disturbance caused by the measurement chain itself

To carry out a measurement, it is necessary to create an interaction between the measuring instrument and the medium under study. In a temperature measurement, the thermometer exchanges energy with the body under study, thus creating a disturbance in the medium under consideration. In other words, the temperature of a perfectly isolated body is impossible to measure. We have to accept an uncertainty in the system's energy to be able to define its temperature. This thermal disturbance, obvious in all contact measurements, is not, however, non-existent in non-contact methods such as optical pyrometry. To measure the temperature of a black body, a macroscopic opening has to be made in its enclosure, i.e. energy has to be exchanged with the thermometer by radiation.

If it is impossible to cancel out this disturbance, it is essential to minimize it, as otherwise the...