A rotatable powersignal connector includes a fixing part and a rotating part. The wheels are connected to the frame for moving the hand truck place to place. The door includes a guide feature that engages the tray when the tray is moved toward the extended position to stabilize movement of the tray. The volume fraction is preferably is in a range from 0. The resilient spring member transmits the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator shaft is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient movements in opposite directions with respect to the alternator pulley during the driven rotational movement. The filter unit is integrated into at least one of the exchangeable cassettes in order to minimize the amount of maintenance for the analyzer.