Abstract: A transducer is provided for determining the concentration of contaminants in fabric webs. The transducer includes an insulated measuring roller with two electrode rings separated by insulation and extending to the surface of the roller. The roller is supported on swing arms and the electrode rings are connected in the circuit of a conductivity meter. The swing arms cooperate with springs to provide for pressing of the roller against an insulated guiding roller for the fabric web under test. Additional metallic rings can be included in the roller which include temperature sensors used for compensating for the temperature dependency of the conductivity measurement. The guiding roller comprises a metallic roller with an insulating coating. Pairs of the rollers can be included in a device for washing fabric webs.