The standard sine waveform is generated by looking up the sine table , and the triangular carrier waveform is produced by a reversible counter
2.
Compared with digital integrator composed of reversible counter , the trapezoidal formula digital integrator is utilized in integrating element of phase - lock controller , it has advantages in simple realization , fast transient response , wide lock range , insensitivity to disturbance
3.
In its digital processing circuit , clock chip with high precision and temperature compensation is uesd as reference clock . high frequency reversible counter is used to count trimmed impulse signal forward or backward and two pathes saw signals are selected timely by multichannel selector
4.
Therefore , the three fundamentals required to obtain high precise measurements are : 1 ) frequency stability and frequency difference stability of the double - frequency laser source as well as the stable equivalent length of bore ; 2 ) the measuring beam and the reference beam are placed very co - axially ; 3 ) capability of recording the sub - division of the period of phase change and a reversible counter system
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