A multielevational cover for assembling a fluid retaining chamber on a face of an electrophoresis cassette is presented. The turntable comprises a stationary bottom part and a movable top part comprising a platform suitable for receiving a pallet, wherein the movable top part is arranged linearly displaceable in a vertical direction with respect to the stationary bottom part. The system may produce a real-time alert, such as an audible alert, when a concealed object is detected.