An optical sensor device for detecting foreign material in an elongate body, in particular an elongate textile body, comprising a measurement chamber for the elongate textile body, a plurality of light sources (30a - 30c), and a plurality of light detectors (32a - 32c), a support body having - opposing first and second sides (18a, 18b) as well as peripheral sides (20a - 20d) extending transversally to said first and second sides (18a, 18b), - a slit forming said measurement chamber and being open at the first and second sides (18a, 18b), and - light channels (26a - 26f) extending between said measurement chamber and said peripheral sides (20a - 20d), wherein there are - at least one light detector arranged between at least two light sources (30a, 30b) on a first side of said measurement chamber and - at least one light source arranged between at least two light detectors (32b, 32c) on a second side of said measurement chamber, wherein said second side of said measurement chamber is opposite to said first side of said measurement chamber, wherein said light sources (30a - 30c) and said light detectors (32a - 32c) are alternatingly arranged at said light channels (26a - 26f) at said peripheral sides (20a - 20d) said optical sensor device being characterized by a first carrier plate on a first peripheral side of said support body and a second carrier plate on a second peripheral side of said support body, wherein said second peripheral side is opposite said first peripheral side, wherein the light source(s) and light detector(s) (30a, 30b, 32a) on said first peripheral side are mounted to said first carrier plate and the light source(s) and the light detector(s) (30c, 32b, 32c) on said second peripheral side are mounted to said second carrier plate. a measurement chamber for the elongate textile body, a plurality of light sources (30a - 30c), and a plurality of light detectors (32a - 32c), a support body having - opposing first and second sides (18a, 18b) as well as peripheral sides (20a - 20d) extending transversally to said first and second sides (18a, 18b), - a slit forming said measurement chamber and being open at the first and second sides (18a, 18b), and - light channels (26a - 26f) extending between said measurement chamber and said peripheral sides (20a - 20d), - opposing first and second sides (18a, 18b) as well as peripheral sides (20a - 20d) extending transversally to said first and second sides (18a, 18b), - a slit forming said measurement chamber and being open at the first and second sides (18a, 18b), and - light channels (26a - 26f) extending between said measurement chamber and said peripheral sides (20a - 20d), wherein there are - at least one light detector arranged between at least two light sources (30a, 30b) on a first side of said measurement chamber and - at least one light source arranged between at least two light detectors (32b, 32c) on a second side of said measurement chamber, - at least one light detector arranged between at least two light sources (30a, 30b) on a first side of said measurement chamber and - at least one light source arranged between at least two light detectors (32b, 32c) on a second side of said measurement chamber, wherein said second side of said measurement chamber is opposite to said first side of said measurement chamber, wherein said light sources (30a - 30c) and said light detectors (32a - 32c) are alternatingly arranged at said light channels (26a - 26f) at said peripheral sides (20a - 20d) said optical sensor device being characterized by a first carrier plate on a first peripheral side of said support body and a second carrier plate on a second peripheral side of said support body, wherein said second peripheral side is opposite said first peripheral side, wherein the light source(s) and light detector(s) (30a, 30b, 32a) on said first peripheral side are mounted to said first carrier plate and the light source(s) and the light detector(s) (30c, 32b, 32c) on said second peripheral side are mounted to said second carrier plate.