Abstract: A measurement cuvette for detecting at least one fluid constituent of a fluid flowing through the measurement cuvette by means of electromagnetic radiation, includes: a channel, which extends through the measurement cuvette along a channel path extending centrally through the channel; a coupling and detection portion, which extends, between its first longitudinal end and its second longitudinal end, along a linear longitudinal axis, detachably mechanically coupled to a radiation component; a physical orientation structure, which allows detachable mechanical coupling of the measurement cuvette to the radiation component in a predefined desired relative orientation and prevents the detachable mechanical coupling in an undesired relative orientation. The physical orientation structure is arranged and formed between the first and the second longitudinal ends of the coupling and detection portion.

Abstract: The invention relates to a measurement device for determining at least one gas component of a gas present in a measuring chamber of the measuring device, the measuring device comprising a housing enclosing the measuring chamber, at least one housing wall section of which housing being designed as an observation section for detecting electromagnetic radiation emanating from the observation section in a direction away from the measuring chamber, the observation section comprising at least one film layer, and the housing being designed as a plastic injection-moulded housing. The invention is characterised in that the observation section has at least one observation wall component comprising an injection-moulded observation body injection-moulded onto the at least one film layer, and the housing comprises the at least one observation wall component and an injection-moulded frame body injection-moulded onto the observation wall component.