A rotation sensor including: a main rotor that integrally rotates with a rotor to be measured; a sub-rotor that rotates in accordance with rotation of the main rotor with a different number of revolutions from that of the main rotor; a first detector detecting rotation of the main rotor; and a second detector detecting rotation of the sub-rotor. A bioreactor system can include one or more bioreactor modules that can be individually controllable and identifiable. The plug connector comprises a second insulating case provided with a pair of separate guide devices on opposite ends and a pair of separate receiving spaces and a plurality of second electrical contacts received in the second insulating case. Only one compartment can be opened at a time. The icing data is presented to the pilot in a display that alerts him to the icing and accurately shows the depth and shape of the airfoil icing.