The velocity of a photoreceptor belt is measured by sensing the passing of illuminated slits in the belt, as the belt moves in a process direction. Two linear position sensors are positioned so as to view the passing of the illuminated slits. The sensors are aligned in a staggered configuration so that there is an overlap region. The slits are positioned so that as one slit is moving off of a downstream sensor, a second slit is moving over the upstream sensor. The output from an illuminated sensor is alternately switched to the second sensor. The sensor outputs are differentiated to provide an output signal representing a belt velocity. The velocity is compared to said velocity in the belt drive system and error signals generated to compensate for detected changes in the belt velocity.