The invention provides a control device for the separate collection of blood components in output from a blood centrifugation cell. The control device comprises: a support which comprises a recess for containing a duct; a visible-light emitter with a corresponding receiver, which are arranged on opposite sides with respect to the recess for containing the duct; an infrared-light emitter with a corresponding receiver, which are arranged on opposite sides with respect to the recess for containing the duct; and a processor to detect signals acquired by the two receivers, to calculate a ratio between the values of the signals, and to send signals to the means suitable to selectively send the fluid conveyed by the duct into separate collection bags, the means being able to change the bag in which the fluid is collected.