Computer tomography system (2) comprises stationary system (4), moving system (6), two references potentials, and coupler. The moving system is operable to move relative to stationary system. The first reference potential is assigned to the stationary system. The second reference potential is assigned to the moving system. The coupler potentially couples the two references potentials. The coupler includes field coupling component for mechanically contactless potential coupling. The coupler comprises capacitive unit. The coupler is disposed on external wall of the moving system. The apparatus includes measuring device measuring a measured variable identifying potential difference between the two reference potentials. The measuring device captures potential difference at the first references potential as measured variable. The measuring device includes measuring component operating according to same principle as the field coupling component, separation capacitor, amplifier, and regulator. The stationary system comprises stator. The moving system comprises armature.
