1,720,984 research outputs found
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
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
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
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
Optical instrument for thickness measurement
Full text linkIn modern metrology it is increasingly common to find the importance of thickness measurements in the production processes of compact materials (metals, plastics, paper, rubber, etc.). A quick and timely measurement is indispensable in those automated industrial processes capable of modifying the production parameters in real time in order to have the characteristics exactly suitable for the needs. The idea of the development of this kind of instrumentation it is starting from this. The requirements that the system will have to respect, including the importance of having a meter that must not be in contact with the plastic film and that can only be positioned on one side of it. These restrictions require the choice of a measurement methodology to be sought mainly in the optical field
Liquid level measurement through capacitive pressure sensor
Full text linkProperty of fluid and material compatibility limit the level sensor's fabrication, dynamic range and accuracy. Piezoresistive pressure sensing elements with media compatible diaphragm are limited in low pressure dynamic. In contrast, capacitive pressure sensing elements provide better solution in terms of dynamic range. In this paper, liquid level measurement is realized through a capacitive differential pressure sensor. A custom digital synchronous detection is implemented in order to optimize the measurement performances, gaining a sensitivity of 40 ppm/mm. Different operating frequencies have been defined and a DFT based feedback loop is proposed in addition to eliminate the impact of interferences at predefined frequency. The sensor characterization indicates linear response. The maximum error is limited to 0.3 mm in range of 0-200 mm as level displacement
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