A device for monitoring feeding of granules, comprising: a duct (12, 111) defining a granule flow path; and a sensor (100, 200, 300, 400, 500) comprising: at least one radiation source (101, 201, 301, 401, 501), at least one radiation sensor (102, 202, 302, 402, 502), arranged to receive radiation from the radiation source, the radiation source and radiation sensor being adapted to be arranged so that incident radiation from the radiation source to the radiation sensor can be acted upon by the granules, and a sensor body (103, 203a, 203b, 303a, 303b, 403a, 403b, 503a, 503b), in which said radiation source and/or radiation sensor are arranged, wherein the sensor body comprises first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions, which are designed to be arranged on substantially opposite sides of the granule flow path, wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are connected to each other, preferably formed in one piece, and wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are elongated and have a respective proximal portion, connected to each other by a link portion (409, 509), and a respective distal portion, forming free ends, characterized in that the sensor body is insertable through at least one opening in a wall defining the duct, by a distance corresponding substantially to a width of the duct, viewed in a direction of insertion. a duct (12, 111) defining a granule flow path; and a sensor (100, 200, 300, 400, 500) comprising: at least one radiation source (101, 201, 301, 401, 501), at least one radiation sensor (102, 202, 302, 402, 502), arranged to receive radiation from the radiation source, the radiation source and radiation sensor being adapted to be arranged so that incident radiation from the radiation source to the radiation sensor can be acted upon by the granules, and a sensor body (103, 203a, 203b, 303a, 303b, 403a, 403b, 503a, 503b), in which said radiation source and/or radiation sensor are arranged, wherein the sensor body comprises first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions, which are designed to be arranged on substantially opposite sides of the granule flow path, wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are connected to each other, preferably formed in one piece, and wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are elongated and have a respective proximal portion, connected to each other by a link portion (409, 509), and a respective distal portion, forming free ends, characterized in that the sensor body is insertable through at least one opening in a wall defining the duct, by a distance corresponding substantially to a width of the duct, viewed in a direction of insertion. at least one radiation source (101, 201, 301, 401, 501), at least one radiation sensor (102, 202, 302, 402, 502), arranged to receive radiation from the radiation source, the radiation source and radiation sensor being adapted to be arranged so that incident radiation from the radiation source to the radiation sensor can be acted upon by the granules, and a sensor body (103, 203a, 203b, 303a, 303b, 403a, 403b, 503a, 503b), in which said radiation source and/or radiation sensor are arranged, wherein the sensor body comprises first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions, which are designed to be arranged on substantially opposite sides of the granule flow path, wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are connected to each other, preferably formed in one piece, and wherein the sensor body first (203a, 303a, 403a, 503a) and second (203b, 303b, 403b, 503b) portions are elongated and have a respective proximal portion, connected to each other by a link portion (409, 509), and a respective distal portion, forming free ends, characterized in that the sensor body is insertable through at least one opening in a wall defining the duct, by a distance corresponding substantially to a width of the duct, viewed in a direction of insertion.