Abstract: A measuring device is disclosed which is capable of exhibiting increased resolution. The device is constructed to detect a moire fringe produced by two scales as A and B phase signals different in phase by 90.degree. and to convert each of the phase signals into a frequency-modulated signal by means of a carrier of a predetermined cycle to digitally read out the deviation of a phase varied with relative movement between both scales.

Abstract: A position feedback system capable of effectively preventing an NC apparatus from failing in a position signal reading operation due to mechanical vibration of a machine tool or the like, including an up-down counter for counting up or down phase signals supplied from a machine position encoder, a comparator for comparing the counted value with a reference value, and a pulse generator for supplying an up- or down-counting pulse having a time period larger than a minimum time period necessary for the reading operation of the NC apparatus to the comparator to initiate a comparison operation regarding the counter contents which generally reflects the number of phase signals, since spurious noise signals have a tendency to cancel each other out. Based on the comparison, a counting pulse is fed to the NC apparatus and a pulse is applied to the counter to cancel one counted value. The operation is carried out until the counted value becomes the same as the reference value.