The article presents the methodology of thermal imaging tests of a disc brake of a DB Link III rail vehicle performed in field conditions. The test methodology was developed on the example of the above-mentioned vehicle, and the temperature distribution of the brake disc during braking was measured. In the article, particular attention was paid to the configuration of the thermal imaging camera to the actual conditions occurring during the test. It is important because due to the rotating brake disc, it is difficult to verify the temperature value with another contact type measuring device. In exceptional cases, temperature measurement with the use of thermocouples is used, but it requires an extensive additional measuring system, which will significantly extend the time of preparing the vehicle for testing and increase its costs. Although the temperature is measured indirectly with the thermal imager, the correct configuration of the camera settings to the real conditions may affect the measurement error by several percent.