Measurement cuvette and radiation sensor, which can be detachably connected only in a predefined relative orientation

A measuring cuvette for detecting at least one fluid component of a fluid flowing through the measuring cuvette with the involvement of electromagnetic radiation, the measuring cuvette comprising:

• a duct penetrating through the measuring cuvette along a duct path, where the duct path is conceived as penetrating through the duct centrally,
• a first connector formation for connecting a first fluid-conveying line,
• a second connector formation for connecting a second fluid-conveying line, and
• a coupling and detection section between the first and the second connector formation, which
• extends along a straight longitudinal axis between its first longitudinal end which is nearer to the first connector formation and its second longitudinal end which is nearer to the second connector formation,
• is configured at least for irradiation of electromagnetic radiation into a duct region of the measuring cuvette surrounded by the coupling and detection section, and
• is configured for detachable mechanical coupling with a radiation component, comprising a radiation source and/or a radiation sensor of the electromagnetic radiation,
• where the measuring cuvette exhibits a physical orientation structure which allows detachable mechanical coupling of the measuring cuvette with the radiation component in a predetermined desirable relative orientation and prevents it in an undesirable relative orientation,
• wherein the physical orientation structure is arranged and configured between the first and the second longitudinal end of the coupling and detection section at a distance to the longitudinal axis which varies, at least one of, along the longitudinal axis and with a dimension orthogonal to the longitudinal axis which varies along the longitudinal axis;
• wherein the orientation structure extends along the longitudinal axis over more than one third of the dimension.