A material processing apparatus comprises a material processing machine pivotably coupled to a base by a pivot joint that allows pivoting movement of the material processing machine about a pivot axis that is perpendicular to a ground surface. The pivot joint comprises an upper joint part coupled to the material processing machine, and a lower joint part coupled to the base, the upper and lower parts being coupled together by a spindle that defines said pivot axis and about which the upper joint part is rotatable with respect to the lower part. The pivot joint includes a non-contact rotation sensor for detecting an angular position of the upper joint part with respect to a reference position.