DIGITAL DISTANCE MEASURING APPARATUS EMPLOYING MODULATED LIGHT BEAM

An improved distance measuring apparatus of the type that automatically calculates distance to a remote reflection target based upon a measured phase difference between a modulated transmitted light beam and a reflected return beam from the remote target incorporates means for ensuring that phase difference measurements are made only when the amplitude of the demodulated return signal is within predetermined limits and therefore that the desired degree of accuracy for the resulting distance calculation is obtained. Additionallly, means are included for ensuring that successive phase different measurements are taken from time-spaced return signals in order that an average of several measurements are obtained from spaced packets or bunches of reflections ordinarily resulting from scintillations due to changing atmospheric conditions over the beam path length, and that the resultant average measurement more accurately represents the true distance to the remote target site.