| 摘要 |
PURPOSE:To easily detect a beam signal by extracting points of every pi phase among points obtained by sampling a reference AC signal at a specific sampling frequency, and using them as sampled values of the beat signal. CONSTITUTION:The difference signal DELTAf between an AC signal of frequency (f) and the reference signal of frequency f0 is obtained by a differential amplifier 1 and lowered by an auxiliary transformer 2 down to a normal input signal level, and the signal is inputted to an analog input card 3. On the input card 3, the difference signal DELTAf is sampled by a sampling part 4 at the sampling frequency fS=2nf0 (n: integer) specified by a control part 8 such as a microprocessor and then A/D-converted 5. The A/D-converted sampled value is sent to a positive/negative decision part 6 to decide whether the signal is positive or negative, so that the signal is outputted from an output part 7 as a digital sine-wave beat signal.
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