is located in the upper scanner head 98 analysis of the transmitted radiation yields the moisture content exemplary scanning dual head sensors employing radiation source and detectors are described for example in u s pat nos 5 654 799 to chase et al 5 793 486 to gordon et al and 7 494 567 to haran which are incorporated herein by reference while the sensor is illustrated in measuring characteristics of paper it is understood that the sensor can be employed to detect a variety of components in a number of different materials including for example plastics coated materials fabrics and the like interference with the movement of scanner heads 98 102 by foreign bodies can be detected and acted upon where the abnormal occurrence is severe such as in the case of impact by an object the drive system can be shut down immediately less severe situations such as sudden acceleration changes that cause a scanner head to jerk will cause vibrations in the head mountings and drive system that can be detected the motor drive tuning can be adjusted during regular maintenance positioned preferably in the center of upper scanner head 98 is a vibration sensor 128 such as a three axis printed circuit board pcb mounted accelerometer a.