Diagnosis of a thermometer

An apparatus for determining and/or monitoring temperature of a medium in a containment, comprising a measuring insert, in which at least one temperature sensor is arranged, and

• a protective tube, which serves for contacting the medium and for accommodating the measuring insert,
• wherein the apparatus further comprises at least one diagnostic unit, which includes at least a first electrode of a first material, which first electrode is located, at least partially, in an internal volume of the apparatus, and wherein a galvanic cell is formed by the first electrode and one of the following:
• a second electrode comprised by the diagnostic unit, wherein the first material and a second material of the second electrode differ from one another in terms of electrochemical properties;
• the protective tube, wherein the first material differs from a material of the protective tube in terms of electrochemical properties;
• or
• a neck tube for connecting with the protective tube, wherein the first material differs from a material of the neck tube in terms of electrochemical properties;
• and wherein the apparatus is configured such that upon medium entering the apparatus due to a damage of the protective tube, a voltage in the galvanic cell is generated, thereby enabling the diagnostic unit to detect the damage based on the generated voltage.