Abstract: A sensor head-transporting roller carriage has four pairs of wheels acting around pivot points at the four corners of the carriage, which is advanced along tracks that are supported by vertical structures. The lateral wheel spacing is chosen in correlation with the track support interval distances such that the vertical travel of all the wheels together is averaged, to be zero. As a result, variations in displacement alignment of the sensor are minimized. In addition, the pivot mechanism results in a fifty percent reduction in the effect of random vertical deflections caused by track debris or wheel concentricity etc. versus standard non-pivoting wheel sets. The roller carriage moves the sensor head along the cross direction to monitoring physical characteristics of a web of material that is moving in the machine direction.