1. A method for turbidity measurement in a measured medium by means of an apparatus comprising: at least a first and a second emitter, and at least a first detector and a second detector, comprising the steps of: exciting the first and the second emitter one after the other, in order to produce light signals directed into the measured medium, wherein each light signal travels along a first propagation path through the measured medium to the first detector, and is converted by such into a first detector signal; and travels along a second propagation path through the measured medium to the second detector, and is converted by such into a second detector signal; and ascertaining a turbidity value based on the first and the second detector signals by means of at least one additional detector, to which at least one of the light signals travels along an additional propagation path, a supplemental detector signal is ascertained, and on the basis of the additional detector signal, the turbidity value is checked as regards its plausibility, wherein: the plausibility is a probability with which the turbidity value reflects the actual turbidity of the measured medium; and the at least one additional detector receives light signal of at least one emitter along a propagation path outside of the measured medium.