A fan consisting of an electric external rotor motor and of a fan wheel, the external rotor motor consisting of a stator encapsulated with an insulating material, and a rotor carrying the fan wheel enclosing the stator in a pot-shaped manner. The modules 31 to 34 includes a liquid crystal display 31a; a graphic control circuit 32a1 and a navigation control circuit 32a2; an MD unit 33a; and a CD unit 34a, respectively. The ring can be connected rigidly to the support, or can be connected to the support via a ring positioning unit that is able to translate or tilt the gantry relative to the support on one or more axes. The horizontal bore further extends to the vertical bore.