An operator control device has a control panel with a user side facing a user and an inner side facing away from the user. The control panel has an operator control element region. A rotary knob is positioned on the user side of the control panel in the region of the operator control element region and can be rotated about a rotational axis. The rotary knob is detachably attached to the control panel and has an encoder block with a code section which is at a distance, changing along the circumferential direction, from a lower end side, facing the control panel, of the rotary knob. An optical sensor is arranged on the inner side of the control panel in the region of the operator control element region and is configured to sense a distance between the optical sensor and the code section of the encoder block by electromagnetic radiation.