1,721,030 research outputs found
Native signal self-mix interferometer has less than 1 nm noise equivalent displacement
Full text linkWe demonstrate that the native configuration of a self-mixing interferometer attains a minimum detectable displacement of 0.72 nm or λ/1870 at the laser wavelength of 1310 nm, obtained by the bare laser diode package including a monitor photodiode, observed in the electrical domain by means of an oscilloscope and without any electronic processing of the signal
SNR improvement of 8.2 dB in a self-mixing laser diode interferometer by using the difference signal at the output mirrors [Invited]
No full textAt the mirrors of a laser diode self-mixing interferometer, the output beams carry anti-correlated (i.e., in phase opposition) interferometric signals, whereas the superposed noise fluctuations are (partially) correlated. Therefore, by using an instrumental output of the interferometer as the difference of the two, we double the amplitude of the self-mixing useful signal, while the superposed noise is reduced. To validate the idea, we first calculate the noise reduction by means of a secondquantization model, finding that in a laser diode the signal-to-noise ratio (SNR) can be improved by 8.2 dB, typically. Then, we also carry out an experimental measurement of SNR and find very good agreement with the theoretical result
Causes of Error for Turbine Radial Palette Measurement
No full textThis paper describes the project of an optical measurement system, an evolution of the system currently installed on the lathe for turbine palettes refinement in Ansaldo Energie, developed by the Politecnico di Milano. This article analyzes the most significant causes of errors found in designing an optical measurement system, proposing improvements that can optimize the system, both in terms of performance and reliability. The idea behind this work is to develop a system that can measure with an accuracy of 10m the difference of length of palettes of a turbine stadium in real time, while the turbine is turning on a refinement lathe
Interferometric instrument for thickness measurement on blown films
Full text linkReal-time measurement of plastic film thickness during production is extremely important to guarantee planarity of the final film. Standard techniques are based on capacitive measurements, in close contact with the film. These techniques require continuous calibration and temperature compensation, while their contact can damage the film. Different optical contactless techniques are described in literature, but none has found application to real production, due to the strong vibration of the films. We propose a new structure of low-coherence fiber interferometer able to measure blown film thickness during productions. The novel fiber-optic setup is a cross between an autocorrelator and a white light interferometer, taking the advantages of both approaches. View Full-Text
Noise in an FM-Converted Self-Mixing Interferometer
Full text linkWe measure the noise of the converted frequency-modulated (cFM) signal in a self-mixing interferometer (SMI) and confirm the theoretical prediction of a dependence of rms noise from ( 1+ C)-1 , where C is the Acket feedback factor, up to a high value (i.e., C=30 ) in region III of Tkach and Chraplyvy feedback diagram. We also verify the minor dependence of noise from the phase factor 2ks + atan α. Finally, we show that the cFM SMI easily attains an unprecedented limit of small-signal detection, with amplitudes down to 0.25 pm surd Hz
Liquid Level Sensor Based on Phase-Shifting of Radio-Frequency Wave
Full text linkThe presence of liquid slightly changes the local properties of submerged transmission line. A dedicated sensor is presented in this paper to estimate the level of liquid, through two different determinations: measurement of the overall capacitance of a bi-wires and time of flight estimation of electromagnetic radiation. Since two measurement methods are physically independent, the proposed sensor has an intrinsic redundancy. The level of liquid is measured through phase shift: the signals are sampled at a sufficiently high frequency and then phase differences is evaluated by calculating the coefficients of the digital Fourier transform. Both measurements are performed directly in baseband without requiring frequency conversions. In contrast with typical TDR system where the end of the cable is open or short-circuited, the bi-wires fold and return to the measurement electronics. The characterization of the proposed sensor is determined experimentally for water and diesel fuel, in good agreement with simulation results. As results show, both phase-shifting measurements are linear with the liquid level, providing a resolution in the order of 0.1 mm through a compact and low-cost realization
Active Protection System for Safety Stop Mechanism in Portable Cutting Tools
No full textAchieving a comprehensive protection system associated with unpredictability of human behavior, complexity of the cutting task and variety of the environmental working condition, is a task, which presents a considerable challenge. To address such difficulties, this article presents an effective detection algorithm based on the measurement of impedance between the bar of chainsaw and the rear handle, extended by the human body. A multitone signal has been exploited to evaluate the system's response and validate the equivalent electrical model experimentally. To evaluate the transfer function, discrete Fourier transform is performed, and the Fourier coefficients are evaluated by multiplying the acquired signals by two vectors of sine and cosine at four frequencies. As results show, the magnitude of the transfer function carries information about the approaching distance, while phase provides very useful information to distinguish between the proximity to body instead of tree. Finally, the developed algorithm demonstrates a successful human body detection rate of 100% with 4% of false-positive detections
Differential Pressure-Based Densitometer in Dynamic Condition
Full text linkChange in density will cause errors in measurement for indirect-based level sensing approaches, such as capacitive sensors. In addition, there is growing attention in measuring density accurately not only in laboratory conditions but also in a real-time dynamic environment. To address the above-mentioned issues, an independent instrument based on differential pressure sensors is proposed in this article. Synchronous detection is used to detect the desired signal by calculating the coefficients of the digital Fourier transform. The characterization of the sensor is experimentally determined under a steady-state condition, where a linear response is observed. The thermal behavior of the proposed sensor is studied and compensated using the polynomial fitting technique. Evaluating the uncertainty due to reference values, linearity, and repeatability, the obtained results show a combined uncertainty lower than 7.5 (mg/cm3), mainly limited by observed asymmetric hysteresis at higher temperatures
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