A novel fiber-optic liquid sensor was proposed for simultaneously measuring some liquid properties such as
concentration, refractive index, surface tension, contact angle and viscosity. Based on the effect of surface tension, tested
liquid around fiber probe was pulled upward by the probe. When the balance between the surface tension and gravity
was broken, a liquid drop was formed on the end face of the probe. The liquid drop can be regarded as a plane-convex
lens, and the light transmission path was affected by the geometrical parameters and refractive index of the drop. The
liquid samples (alcohol, water, oil and sucrose) were analyzed using FDLAT. The experimental results indicated that
FDLAT can be used for liquid testing and monitoring.
A fiber optic bending sensing system that uses twin-core fiber as the sensing element has been proposed and
demonstrated. The twin-core fiber act as a two-beam interferometer in which phase differences is a function of the
curvature, and it can be demodulated by the shift of the unique identification spectrum. By way of FFT analysis of the
white light interferometric spectrum, the variation of bending can be measured. The relationship between the bending
curvature and the shift of the unique identification spectrum has been given and the experimental results were also
confirmed this.
KEYWORDS: Demodulation, Interferometers, LabVIEW, Data acquisition, Vibrometry, Signal to noise ratio, Analog electronics, Reflectors, Laser systems engineering, Phase modulation
This paper presented signal demodulation scheme of the laser vibration interferometer system using for measurement of
low-frequency vibration. Based on principle of phase generated carrier (PGC) modulation and virtual instrument
technology, laser vibration signal demodulation on software and hardware platform were established. Taking the
PCI6221 multi-function data acquisition device as the core of hardware circuit, real time data acquisition of reference
waveform generation and the signal for measurement was realized. Digital PGC algorithm was established by using
LabVIEW software workbench, and then vibration signal real time demodulation was realized. The experiment results
indicate that the PGC signal demodulation scheme based on virtual instrument technology reduced drift and noise by
traditional analog PGC hardware circuit such as analog multiplier and differentiator, enhanced accuracy of signal
demodulation, improved system Signal-to-Noise. High accuracy measurement of the low-frequency vibration signals
ranging from 10~200Hz comes true, the measuring resolution is better than 0.5nm, and the dynamic range is 110dB.
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