1,720,983 research outputs found
Health Indicator Effectiveness in Localized Fault Diagnosis: Rolling bearing elements
No full textConstant tracking of a state indicator curve derived from signal features defines the main body of the prediction in the remaining useful life of assert or its components. In this paper, the effectiveness of the pre-processing techniques to extract suitable health indicators and trace fault degradation on rolling element bearing is studied on a practical dataset. As a first step, the envelope analysis is performed to evaluate characteristic frequencies associated with inner and outer race faults. Then, its amplitude spectrum’s effectiveness as a health indicator regarding the fault evaluation is analyzed. As results show, due to the non-stationary nature of the vibration signal, this approach can be used to identify the type of fault in addition to the Root Mean Square value as the main health indicator to have an estimation on the level of degradation of bearing
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
Characterization of Pressure Sensor for Liquid-Level Measurement in Sloshing Condition
Full text linkTo achieve a reliable and accurate liquid-level detection, a differential pressure-based instrument is proposed in this article. The phase-sensitive demodulation of the signal is performed by the discrete Fourier transform (DFT) through a microcontroller. A good linearity in both ac and dc measurements has been observed. AC-based-level sensing demonstrated reliable and robust-level detection compared with dc, in both steady state conditions and while experiencing turbulence on the surface. In addition, thermal behavior of the proposed instrument is characterized and compensated, in order to evaluate its uncertainty as a liquid-level sensor. The obtained results show a combined uncertainty lower than 1 mm, which is mainly limited by sloshing conditions
Electronic Safety System for Table Saw
Full text linkThis article proposes a safety sensor for table saw, based on impedance measurement between two electrodes placed in front of blade. A multitone system is developed, acting as a selective barrier able to distinguish the proximity of a hand with respect to wood, both dry and wet. Due to conductivity of human body, the proximity of the hand introduces a shielding effect, causing a reduction in capacitive coupling between electrodes. On the contrary, wood cannot induce the same effect for all frequencies, even if it is wet. This results in achieving a very sensitive and cost-effective safety system, able to respond effectively to hazard situations. An electronic prototype, realized through digital synchronous detection of two tones at 10 kHz and 1 MHz, demonstrates the effectiveness of the proposed sensing technique. To better describe the working principles, a simple system simulator is studied, able to describe the experimental results. The proposed technique opens the way to a new generation of safety systems for table saw
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
Noise Decrease in a Balanced Self-Mixing Interferometer: Theory and Experiments
Full text linkIn a self-mixing interferometer built around a laser diode, the signals at the outputs of the two mirrors are in phase opposition, whereas noise fluctuations are partially correlated. Thus, on making the difference between the two outputs, the useful signal is doubled in amplitude and the signal-to-noise ratio is even more enhanced. Through a second-quantization model, the improvement is theoretically predicted to be dependent on laser facets reflectivity. The results are then validated by experimental measurements with different laser types that show very good agreement with theoretical results. The new technique is applicable to a number of already existent self-mixing sensors, potentially improving significantly their measurement performances
Remote reflectivity sensor for industrial applications
Full text linkA low-cost optical reflectivity sensor is proposed in this paper, able to detect the presence of objects or surface optical properties variations, at a distance of up to 20 m. A collimated laser beam is pulsed at 10 kHz, and a synchronous digital detector coherently measures the back-diffused light collected through a 1-inch biconvex lens. The sensor is a cost-effective solution for punctual measurement of the surface reflection at different distances. To enhance the interference immunity, an algorithm based on a double-side digital baseline restorer is proposed and implemented to accurately detect the amplitude of the reflected light. As results show, the sensor is robust against ambient light and shows a strong sensitivity on a wide reflection range. The capability of the proposed sensor was evaluated experimentally for object detection and recognition, in addition to dedicated measurement systems, like remote encoders or keyphasors, realized far from the object to be measured
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