A sensor device and method for detecting the turbidity of wash liquor. The sensor device includes an optical transmitter; an optical receiver, wherein the wash liquor to be tested flows between the transmitter and the receiver; and an electronic control and evaluation device to (a) carry out a reference measurement by means of the optical transmitter and receiver in order to determine a reference measured value; (b) carry out a turbidity measurement on the wash liquor to be measured by means of the optical transmitter and receiver in order to determine a test measured value; (c) relate the reference measured value to the test measured value; and (d) determine a characteristic value for a determined turbidity of the wash liquor therefrom and transmit the characteristic value as a measurement signal. The determination of the reference measured value and the test measured value include determining a gradient of the turbidity.