Sensor

A sensor includes: a transmitting device which transmits radiation along a path to a medium, and a measuring device which receives measuring radiation resulting from an interaction of the transmitted radiation with the medium and determines a measurand of the medium, with which at least one property of the transmitted radiation interacting with the medium can be determined and/or monitored in a cost-effective, space-saving manner; a prism in the path, through which prism a first portion of the transmitted radiation propagates in the direction of the medium and at which a second portion of the transmitted radiation is reflected; and a reference detector which receives the second component reflected at the prism and provides an output signal representing at least one property of the second component of the transmitted radiation.