Laser system preset unit

Claim 1

In a Zeeman-effect laser interferometer system for measuring displacement of an object along an axis including a laser head having a reference signal output for producing pulses at a fixed rate and a Doppler signal output for producing pulses at a rate greater than the rate of said fixed rate pulses for displacement in a forward direction and less than the rate of said fixed rate pulses for displacement in a reverse direction and a digital display unit for detecting differences in the Doppler signal rate relative to the pulse rate of said reference signal for calculating and displaying the displacement of said object along said axis from a reference point, a display preset circuit, comprising: a selectable frequency oscillator; pulse-shaping means connected to the output of said oscillator for generating a fixed period pulse at an output thereof at a repetition rate equal to the frequency of said oscillator, said fixed period being substantially equal to the period of said reference signal and said Doppler signal; a first gating means having an enabling input for coupling the reference signal output of said laser head to the reference signal input of said display unit; a second gating means having enabling input for coupling the Doppler signal output of said laser head to the Doppler signal input of said display unit; and switching means for selectively applying said fixed period pulses to either the enabling input of said first gating means or the enabling input of said second gating means so that the selected gate is disabled for at least the period of one reference or Doppler pulse for each fixed period pulse until the valve to be preset into the display unit is obtained .