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1887

access icon free Accuracy study for lock-in amplifiers in a scanning near-infrared spectrometer

© The Institution of Engineering and Technology
Received 26/10/2016, Accepted 25/05/2017, Revised 30/04/2017, Published 13/06/2017

When a lock-in amplifier was employed in a scanning near-infrared spectrometer, there was the problem of low signal-to-noise ratio (SNR) of spectra. This study investigates the impact of unstable measured signal frequency in the lock-in amplifier. The analysis concludes that when the frequency of the measured signal and reference signal are not equal due to frequency fluctuations, the amplitude detection results are inaccurate and change periodically with the initial phase of the measured signal. According to analysis results, a zero-phase detection method is designed in the spectrometer, where the measured signal phase is judged to guarantee detection starting at the zero-phase position. The experimental results indicate that the average of the SNR of spectra is 2376 using the zero-phase detection method, which is approximately three times that of the original system and coincides with the results of the theoretical calculation (2273) and simulation analysis (2234).

Inspec keywords: amplifiers; phase measurement; infrared spectrometers; phase detectors

Other keywords: reference signal measurement; zero-phase detection method; scanning near-infrared spectrometer; lock-in amplifier; signal-to-noise ratio; SNR; amplitude detection

Subjects: Phase and gain measurement; Modulators, demodulators, discriminators and mixers; Amplifiers

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