Thermometer with a diagnostic function

A device for determining and/or monitoring a temperature of a medium, the device comprising:

• a temperature sensor configured to detect the temperature of the medium, wherein the temperature sensor includes a temperature-sensitive sensor element;
• an electronics module, wherein the temperature-sensitive sensor element is in electrical contact with the electronics module via at least one connection line, wherein:
• the at least one connection line includes a first connection line and a second connection line,
• the temperature sensor is electrically contacted via the first connection line and the second connection line,
• the first connection line is divided into a first section and a second section,
• the first section, which faces the sensor element, consists essentially of a first material,
• the second section, which faces away from the sensor element, consists essentially of a second material, which differs from the first material,
• the second connection line consists essentially of the second material,
• the first section of the first connection line and at least a part of the second connection line form a first differential temperature sensor in the form of a thermocouple in a region of the temperature-sensitive sensor element;
• and
• a diagnostic unit configured for temporal variation of a power of an input signal, by which the temperature sensor or at least one component of the device can be acted upon, wherein the diagnostic unit is further configured to determine, based on an output signal of the temperature sensor in response to the input signal, a statement about a thermal coupling of the temperature sensor to the medium.