Apparatus for optical in-situ gas analysis

An apparatus for optical in-situ gas analysis, comprising

• a housing;
• a measuring lance having a first end and a second end, with the first end being connected to the housing, with the second end projecting into the gas to be measured and with the measuring lance having an optical path;
• a light transmitter that is arranged in the housing and with the light from the light transmitter being conducted into the measuring lance;
• a light receiver which receives light reflected by a reflector arranged at the second end, with the optical path defining an optical measurement path within the measuring lance;
• an evaluation device for evaluating received light signals of the light receiver;
• and
• a test gas connection via which test gas can be conducted into the measurement path,
• wherein the measuring lance has an outer tube and the outer tube has openings for the gas to be measured;
• wherein the openings can be closed by at least one seal and with the at least one seal sealingly closing the openings by enlarging its volume.