Showing papers on "Pressure measurement published in 2019"

In-situ monitoring of polymer flow temperature and pressure in extrusion based additive manufacturing

Abstract: We demonstrate a novel Fused Filament Fabrication (FFF) nozzle design to enable measurements of in-situ conditions inside FFF nozzles, which is critical to ensuring that the polymer extrudate is flowing at appropriate temperature and flow rate during the part build process. Testing was performed with ABS filament using a modified Monoprice Maker Select 3D printer. In-situ measurements using the printer’s default temperature control settings showed an 11 °C decrease in temperature and significant fluctuation in pressure during printing as well as fluctuations while idle of ± 2 °C and ±14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated proportional–integral–derivative (PID) system. At the highest tested flow rates, decreases in melt temperature as high as 6.5 °C were observed, even with a properly calibrated PID, providing critical insight into the significance of flow rate and PID calibration on actual polymer melt temperature inside the FFF nozzle. Pressure readings ranging from 140 to 6900 kPa were measured over a range of filament feed rates and corresponding extrusion flow rates. In-situ pressure measurements were higher than theoretical predictions using a power-law fluid model, suggesting that the assumptions used for theoretical calculations may not be completely capturing the dynamics in the FFF liquefier. Our nozzle prototype succeeded in measuring the internal conditions of FFF nozzles, thereby providing a number of important insights into the printing process which are vital for monitoring and improving FFF printed parts.

Flexible capacitive pressure sensor with sensitivity and linear measuring range enhanced based on porous composite of carbon conductive paste and polydimethylsiloxane

Abstract: In recent years, the development of electronic skin and smart wearable body sensors has put forward high requirements for flexible pressure sensors with high sensitivity and large linear measuring range. However, it turns out to be difficult to increase both of them simultaneously. In this paper, a flexible capacitive pressure sensor based on a porous carbon conductive paste-polydimethylsiloxane composite is reported, the sensitivity and the linear measuring range of which were developed using multiple methods including adjusting the stiffness of the dielectric layer material, fabricating a microstructure and increasing the dielectric permittivity of the dielectric layer. The capacitive pressure sensor reported here has a relatively high sensitivity of 1.1 kPa-1 and a large linear measuring range of 10 kPa, making the product of the sensitivity and linear measuring range 11, which is higher than that of the most reported capacitive pressure sensors to our best knowledge. The sensor has a detection of limit of 4 Pa, response time of 60 ms and great stability. Some potential applications of the sensor were demonstrated, such as arterial pulse wave measuring and breath measuring, which shows it as a promising candidate for wearable biomedical devices. In addition, a pressure sensor array based on the material was also fabricated and it could identify objects in the shape of different letters clearly, which shows promising application in future electronic skins.

Ultra-robust wide-range pressure sensor with fast response based on polyurethane foam doubly coated with conformal silicone rubber and CNT/TPU nanocomposites islands

Abstract: Highly durable piezo-resistive pressure sensors with excellent repeatability and fast response were developed. The developed sensor have a characteristic of coated with silicone rubber, which has widened pressure measurement range and improved response time. The sensor is capable of measuring pressures lower than 100Pa and higher than 200 kPa and can measure oscillating pressure well above 50 Hz. The sensor showed high repeatability and durability and operated normally after 1000 cycles at 360 kPa applied pressure. The sensor was made by coating polyurethane foam with silicone rubber and further dip-coated with MWCNT dispersed TPU ink. The use of TPU as a binding material helped MWCNT strongly attach to the foam skeleton and reduced the interfacial electrical resistance. As a result, low hysteresis (6.4%) was achieved. By controlling amount of silicone rubber impregnated, the sensitivity can be controlled from 0.013 kPa−1 to 0.032 kPa−1. These sensors were used for measuring both subtle pressures such as the pulse and large pressures such as the pressure beneath a heel. Additionally, wide range of pressure distributions were measured using the array sensors. The economic value of this sensor is tremendous because it can be used in a wide pressure range where high repeatability and fast response are required.

A flexible ionic liquid-polyurethane sponge capacitive pressure sensor

Abstract: A flexible microfluidic polyurethane sponge super-capacitive pressure sensor is developed to measure the pressure. The innovative sensor contains a polyurethane sponge filled with ionic liquid dielectric layer, and coated with two indium tin oxide polyethylene terephthalate (ITO-PET) films on the top and bottom, respectively. When external pressure is applied on the sensor, the contact area between ITO-PET electrode and ionic liquid polyurethane sponge (ILPU) dielectric layer increases and the distance between two ITO-PET electrodes decreases due to the structural deformation, resulting in the capacitance of the sensor increasing rapidly. The external pressure will be determined based on the change of capacitance. Comparing to traditional pressure sensor, the developed sensor provides a high sensitivity up to 5.28 nF/KPa and rapid dynamic responses for pressure measurement. Experiments are also conducted to investigate the influence of the temperature and humidity.

Modeling of interlayer contact and contact pressure during fused filament fabrication

Abstract: An in-line rheometer and data acquisition system are used to monitor the melt pressure, melt temperature, and environmental temperatures while producing parts via fused filament fabrication (FFF). Melt pressures are observed to increase when printing parts with small layer heights, which is attributed to the confined space created between the nozzle and the previous layer (i.e., an exit pressure). These exit pressures (referred to as contact pressure) and the resulting interlayer contact areas are analyzed for 2863 layers created at 21 different processing conditions. The measured contact pressure was found to directly influence the shape of the layers and the resulting interlayer contact. An intimate contact model based on contact pressure is combined with a wetting model to accurately predict the interlayer contact of FFF parts. This pressure-driven intimate contact model for FFF shows strong agreement with the observed interlayer contact. No theoretical model has previously existed for predicting interlayer contact, so this research provides a critical component for developing a comprehensive part strength model. Both the measurements and proposed model are sufficiently simple and accurate for real-time analysis of FFF quality, so the described in-line sensors provide valuable quality insights and are recommended for future researchers, printer manufacturers, and end-users.

Flexible piezoresistive sensor matrix based on a carbon nanotube PDMS composite for dynamic pressure distribution measurement

Abstract: . A highly flexible, piezoresistive sensor matrix based on a carbon nanotube (CNT) polymer composite is developed for pressure distribution measurement applications. With an overall height of about 400 µ m, the sensors can measure pressure directly, without any deformation elements, such as a cantilever or a deformation membrane. The measurement range is from 2.5 to 640 kPa. Both the position and the pressure of the applied load can be measured and visualized as a resistance change. The relative resistance measurement deviation of the data acquisition system is lower than 3 % for the resistance range of 610Ω to 380 k Ω . This corresponds to a systematic deviation of pressure measurement of less than 3 % in the measurement range. Besides the measurement of pressure, different sizes of loads can be detected as well. The developed fast and compact measurement system allows dynamic pressure measurement, such as gait analysis when used in an insole application.

Fiber Optic Fabry-Perot Pressure Sensor With Embedded MEMS Micro-Cavity for Ultra-High Pressure Detection

Abstract: A fiber-optic Fabry–Perot pressure sensor with embedded micro-electromechanical system (MEMS) micro-cavity for ultra-high pressure detection is demonstrated. The embedded-type structure (ETS) is first proposed and analyzed to meet the requirements of ultra-high pressure detection. The geometry parameters of sensor have been optimized by analyzing mechanical and optical characteristics. From the analysis results based on the ETS, an ultra-high pressure sensor is fabricated and experimentally demonstrated for ultra-high pressure detection. The ultra-high pressure experiment illustrated response relationship between the absolute phase and pressure in the range of 2–120 MPa, and full-scale (FS) errors less than 0.079% F.S. at room temperature. The other characteristics index of sensor such as pressure sensitivity, hysteresis error, and temperature's influence factor are superior to 1.071 rad/MPa, 1.397%, and $\text{2.665} \times {\text{10}^{ - \text{3}}}{\text{ rad}}/^\circ {\text{C}}$ , respectively. The transient response time of system is 0.27 s. The sensor can be used for ultra-high pressure detections, which is necessary in deep-sea and oil exploration.

Antiresonant mechanism based self-temperature-calibrated fiber optic Fabry─Perot gas pressure sensors

Abstract: A self-temperature-calibrated gas pressure sensor with a sandwich structure made of single-mode fiber (SMF)-hollow core fiber (HCF)-SMF is proposed and experimentally demonstrated. A Fabry-Perot interferometer (FPI) is formed by the SMF-HCF-SMF structure along the axial direction, and an antiresonant reflecting optical waveguide (ARROW) is formed by the ring-cladding of the HCF along the radial direction. A micro-channel is drilled on the ring-cladding of the HCF using a femtosecond laser to facilitate air entering/exiting the HCF. The FPI functions as the pressure sensor, and the ARROW functions as the temperature sensor. The initial wavelength and pressure sensitivity of the FPI can be calibrated from the temperature obtained by measuring the optical thickness of the ARROW. The experimental results show that the ARROW exhibits a temperature sensitivity of ~0.584 nm/°C, and the pressure sensitivity of the FPI ranges from 3.884 to 0.919 nm/MPa, within the temperature range of 37-1007 °C. The simplicity and durability of the sensor make it suitable for reliable gas pressure measurement in high-temperature environments.

Fiber-optic Fabry-Perot pressure sensor based on sapphire direct bonding for high-temperature applications.

Abstract: In this study, a fiber-optic Fabry–Perot (FP) high-temperature pressure sensor based on sapphire direct bonding is proposed and experimentally demonstrated. The sensor is fabricated by direct bonding of two-layer sapphire wafers, including a pressure diaphragm wafer and a cavity-etched wafer. The sensor is composed of a sensor head that contains a vacuum-sealed cavity arranged as an FP cavity and a multimode optical fiber. The external pressure can be measured by detecting the change in FP cavity length in the sensor. Experimental results demonstrate the sensing capabilities for pressures from 20 kPa to 700 kPa up to 800°C.

Pressure from 2D snapshot PIV.

Abstract: In this study, we quantify the accuracy of a simple pressure estimation method from 2D snapshot PIV in attached and separated flows. Particle image velocimetry (PIV) offers the possibility to acquire a field of pressure instead of point measurements. Multiple methods may be used to obtain pressure from PIV measurements, however, the current state-of-the-art requires expensive equipment and data processing. As an alternative, we aim to quantify the efficacy of estimating instantaneous pressure from snapshot (non-time resolved) two-dimensional planar PIV (the simplest type of PIV available). To make up for the loss of temporal information, we rely on Taylor’s hypothesis (TH) to replace temporal information with spatial gradients. Application of our approach to high-resolution 2D velocity data of a turbulent boundary layer flow over ribs shows moderate to good agreement with reference pressure measurements in average and fluctuations. To assess the performance of the 2D TH method beyond average and fluctuation statistics, we acquired a time-resolved measurement of the same flow and determined temporal correlation values of the pressure from our method with reference measurements. Overall, the correlation attains good values for all measured locations. For comparison, we also applied two time-resolved approaches, which attained values of correlation similar to our approach. The performance of the 2D TH method is further assessed on 3D time-resolved velocity data for a turbulent boundary layer and compared with 3D methods. The root-mean-square (RMS) pressure fluctuations of the 2D TH, 3D TH and 3D pseudo-Lagrangian methods closely follow the pressure fluctuation distribution from DNS. These observations on the RMS pressure estimates are further supported by similar analysis on synthetic PIV data (based on DNS) of a turbulent channel flow. The values of spatial correlation between the 2D TH method and the DNS pressure fields in this case, are similar to the temporal correlations achieved in the turbulent flow over the ribs. Finally, we discuss the accuracy of instantaneous pressure estimates and provide a rule of thumb to determine regions where the pressure fluctuation estimate from the 2D TH methods is likely to fail.

Highly Sensitive FBG Pressure Sensor Based on a 3D-Printed Transducer

Abstract: In this work, we describe a fiber Bragg grating (FBG) pressure sensor with high sensitivity. The sensor exploits a three-dimensional printed mechanical transducer capable of converting the external pressure very efficiently into strain, measured by a first FBG, whereas a second one is used for temperature compensation. The pressure sensitivity of this sensor is found as high as 240 pm/kPa with an accuracy of 112 Pa over 10 kPa, which makes this sensor up to 80,000 times more sensitive than a bare fiber Bragg grating. Moreover, it is experimentally shown that it is capable of detecting fast dynamic pressure change up to 100 Hz. Thanks to these performances, this device can be used in many static and dynamic low-pressure measurement applications, and it is here demonstrated as a sub-millimetric surface water waves detector.

Simple fiber-optic sensor for simultaneous and sensitive measurement of high pressure and high temperature based on the silica capillary tube.

Abstract: A simple fiber-optic sensor for simultaneous measurement of high pressure and high temperature was proposed. The sensor was simply fabricated by splicing two sections of silica capillary tubes (SCTs) with different inner diameters to the single-mode fiber. The thick core SCT functions as a Fabry-Perot (FP) micro-cavity and an anti-resonant reflecting waveguide at the same time. The two different sensing mechanisms lead to the high contrast sensitivity values of pressure and temperature (‒3.76 nm/MPa, 27.7 pm/°C and 4.24 nm/MPa, 0.82 pm/°C). We also proposed a simple and effective method to evaluate the actual sensitivities of two-parameter sensors by using linear programming, which shows that our sensor is more sensitive than others in high pressure and high temperature simultaneous detection. Besides, low cost, good mechanical property and convenient reflective probe make the sensor more competitive in actual application.

Screen-Printed Piezoresistive Sensors for Monitoring Pressure Distribution in Wheelchair

Abstract: Prolonged sitting inadequacies cause pressure ulcer to many individuals, especially to disadvantaged with reduced mobility. The measurement of distributed pressure and detection of irregular sitting postures is essential for preventing the risk of developing pressure ulcer. In this paper, a pressure sensing system capable of recognizing sitting postures by means of measuring interface pressure through printed pressure sensors is presented. A thin and flexible large area sensor is screen-printed using silver flake and carbon particle inks and comprises 16 sensing elements. For the evaluation of practical usability, the sensor characterization is carried out by conducting stability, repeatability, drift, and bending tests. The performance of the sensor is checked under varying environmental conditions. Sitting posture detection accuracy above 80 % is achieved using a classification algorithm for four different sitting postures. Pressure distribution is monitored at a scanning rate of 10 Hz. A low-power and small form factor of readout electronics enables a compact packaging inside the seat cushion. The presented sensor design targets smart wheelchairs, but it is extendable to much larger areas, for example, to be used in beds. The proposed sensing system would be of a great assistance for caregivers and health professionals.

New Near-Wellbore Insights from Fiber Optics and Downhole Pressure Gauge Data

Abstract: It has been widely demonstrated that frac stimulation efficiency and more importantly production, varies significantly between perforation clusters as well as between sleeve entries. Recent trends indicate that many operators are simultaneously increasing the number of perforation clusters or entries while decreasing frac-to-frac spacing. This is done with the expectation that it will lead to more productive wells overall. The purpose of this paper is to investigate some of the aspects that may limit this approach. There are an increasing number of frac diagnostic tools which allow us to get a better understanding of frac placement and production. Unfortunately, there are only few diagnostic tools available today to characterize the near wellbore region (NWR). Fiber Optics (FO) and other downhole measurements can play an important role in providing information about the NWR. In this paper, we share data and examples from wells where the combination of data from Distributed Acoustics Sensing (DAS), Distributed Temperature Sensing (DTS) and downhole gauges is helping us gain insights about this poorly understood region of our unconventional reservoirs. This paper combines DAS, DTS and downhole pressure gauge data to demonstrate the existence of significant near wellbore complexity, both during stimulation and production. We frequently observe changes in DAS signal and pressure during the stimulation of horizontal wells completed via both "Plug and Perf" (PnP) and Cemented Single Point Entry (CSPE) systems. These changes support the existence of significant near-wellbore tortuosity. Furthermore, we show that pressure data from downhole gauges can differ significantly from surface pressure data extrapolated downhole. This can impact the interpretation of Step-Down-Tests, other analytical techniques relying on the surface pressure alone and affecting the calibration of frac models aimed at understanding the NWR. In wells instrumented with a FO cable behind casing, it is possible to use the DTS data during warmback, following stimulation injection to gain insights about frac geometry in the NWR. Such data provides information about the hydraulic frac dimensions created by the stimulation process in both vertical and horizontal wells. During warmback it is easy to distinguish intervals containing hydraulic fractures near the wellbore where the temperature recovery is lagging compared to the unstimulated portions of the well. FO instrumented horizontal wells allow for estimation of the dimensions of the "Frac-Zone" along the wellbore in the NWR where a combination of hydraulically induced longiditunal and vertical transverse fracs exist. Thermal modeling is also presented for selected stages that further support the qualitative interpretation of the DTS. The diagnostics presented help quantify the dimensions of longitudinal and transverse components in horizontal wellbores in the NWR. This paper also highlights the risk of putting perforation clusters or sleeve entries too close to one another. It is clear that the NWR is poorly understood and more information is needed. Understanding the processes that govern the NWR are essential, after all, this is the region where the well and the reservoir interact.

Considerations for Choosing Sensitive Element Size for Needle and Fiber-Optic Hydrophones—Part II: Experimental Validation of Spatial Averaging Model

Abstract: Acoustic pressure can be measured with a hydrophone. Hydrophone measurements can underestimate incident acoustic pressure due to spatial averaging effects across the hydrophone sensitive element. The spatial averaging filter for a nonlinear focused beam is a low-pass filter that decreases monotonically from 1 to 0 as frequency increases from 0 to infinity. Experiments were performed to test an analytic model for the spatial averaging filter. Nonlinear pressure tone bursts were generated by three source transducers with driving frequencies ranging from 2.5 to 6 MHz, diameters ranging from 19 to 64 mm, and focal lengths ranging from 38 to 89 mm. The nonlinear pressure fields were measured using four needle hydrophones with nominal geometrical sensitive element diameters of 200, 400, 600, and $1000~\mu \text{m}$ . The average root-mean-square difference between theoretical and experimental spatial averaging filters was 5.8% ± 2.6%.

Fabry–Perot Interferometer-Based Absolute Pressure Sensor With Stainless Steel Diaphragm

Abstract: In this paper, we discuss the design, fabrication, and testing of an external Fabry–Perot interferometer (EFPI)-based absolute type fiber optic pressure sensor of range 0–50 mbar. The FPI has sapphire as the first reflecting surface and stainless steel (SS) sheet (SS316L of thickness 0.18 mm) as the second one. In order to achieve high specular reflectivity, the reflecting surface of sapphire is coated with a broad band thin film coating, while the SS316L sheet is surface finished with the Chemo Mechanical Magneto Rheological finishing process. The parallelism between two reflecting surfaces of FPI and their individual flatness is around $\lambda $ /15, which was achieved by precision machining and assembly with stretched diaphragm. The SS sheet also works as the deflecting diaphragm of the pressure sensor and causes change in the FPI gap with applied pressure. FPI gap is calculated from the reflected spectrum by an improvised yet simple scheme. In this paper, FPI is an enclosed cell with vacuum inside, which acts as the reference pressure of the sensor. Applied pressure of 0–50 mbar changed the FPI gap by around $17~\mu \text{m}$ . This sensor was tested with white light interferometric technique, and the best finesse obtained was 5.5. The proposed device is an optical analogous of a capacitance-based pressure sensor. To the best of our knowledge, FPI-based absolute pressure sensors of sub-atmospheric range with a metal diaphragm have not been reported anywhere.

Piezoresistive thin film pressure sensor based on carbon nanotube-polyimide nanocomposites

Abstract: A novel ring-shaped piezoresistive pressure sensor is designed, fabricated and characterized in this paper. Carbon nanotube (CNT)-polyimide (PI) nanocomposites with different CNT concentrations are prepared in a liquid mixture as the fabrication material. The ring-shaped nanocomposite thin film device is deposited on a circular polyimide diaphragm by inkjet printing fabrication method. The drop-on-demand fabrication process of the inkjet printer enables the fabrication of nanocomposite thin film in various geometries and shapes to achieve better structural compatibility with the sensor port and overall measurement accuracy. The equivalent circuit parameters of the nanocomposite thin film device are derived through electrical impedance measurement. The sensitivity of the ring-shaped CNT-PI pressure sensor is investigated, and the gauge factors under static pressure are characterized using a pressure tube. The results demonstrate that this novel ring-shaped nanocomposite thin film pressure sensor can be used for pressure measurement with easy fabrication process, excellent flexibility and high sensitivity.

Measured relationship between thermodynamic pressure and refractivity for six candidate gases in laser barometry.

Abstract: Laser refractometers are approaching accuracy levels where gas pressures in the range 1 Pa < p < 1 MPa inferred by measurements of gas refractivity at a known temperature will be competitive with the best existing pressure standards and sensors. Here, the authors develop the relationship between pressure and refractivity p = c 1 ⋅ ( n − 1 ) + c 2 ⋅ ( n − 1 ) 2 + c 3 ⋅ ( n − 1 ) 3 + ⋯, via measurement at T = 293.1529 ( 13 ) K and λ = 632.9908 ( 2 ) nm for p ≤ 500 kPa. The authors give values of the coefficients c 1 , c 2 , c 3 for six gases: Ne, Ar, Xe, N 2, CO 2, and N 2 O. For each gas, the resulting molar polarizability A R ≡ 2 R T 3 c 1 has a standard uncertainty within 16 × 10 − 6 ⋅ A R. In these experiments, pressure was realized via measurements of helium refractivity at a known temperature: for He, the relationship between pressure and refractivity is known through calculation much more accurately than it can presently be measured. This feature allowed them to calibrate a pressure transducer in situ with helium and subsequently use the transducer to accurately gage the relationship between pressure and refractivity on an isotherm for other gases of interest.

A Flexible and Highly Sensitive Inductive Pressure Sensor Array Based on Ferrite Films.

Abstract: There is a rapid growing demand for highly sensitive, easy adaptive and low-cost pressure sensing solutions in the fields of health monitoring, wearable electronics and home care. Here, we report a novel flexible inductive pressure sensor array with ultrahigh sensitivity and a simple construction, for large-area contact pressure measurements. In general, the device consists of three layers: a planar spiral inductor layer and ferrite film units attached on a polyethylene terephthalate (PET) membrane, which are separated by an array of elastic pillars. Importantly, by introducing the ferrite film with an excellent magnetic permeability, the effective permeability around the inductor is greatly influenced by the separation distance between the inductor and the ferrite film. As a result, the value of the inductance changes largely as the separation distance varies as an external load applies. Our device has achieved an ultrahigh sensitivity of 1.60 kPa−1 with a resolution of 13.61 Pa in the pressure range of 0–0.18 kPa, which is comparable to the current state-of-the-art flexible pressure sensors. More remarkably, our device shows an outstanding stability when exposed to environmental interferences, e.g., electrical noises from skin surfaces (within 0.08% variations) and a constant pressure load for more than 32 h (within 0.3% variations). In addition, the device exhibits a fast response time of 111 ms and a good repeatability under cyclic pressures varying from 38.45 to 177.82 Pa. To demonstrate its practical usage, we have successfully developed a 4 × 4 inductive pressure sensor array into a wearable keyboard for a smart electronic calendar application.

Dependence of neutral pressure on detachment in the small angle slot divertor at DIII-D

Abstract: Local neutral pressure measurements in the closed small angle slot (SAS) divertor [1,2] on DIII-D show a large increase when the divertor plasma shifts from high recycling into detachment. In-tile pressure gauges were installed to measure the pressure in the near- and far-SOL regions to examine the predicted high neutral pressures and compression. Cross-field drift effects lead to ∼ 10 × higher peak neutral pressure in detachment with the ion ∇B drift toward the divertor compared to out of the divertor, with similar pressures in attached conditions. Drifts also play a role in the neutral distribution in the slot while attached but become less pronounced in detachment once gradient drives reduce. Variation in the outer strike point location found higher neutral pressure and detachment at modestly lower main-plasma density with the strike point positioned away from the designed operation point. Reducing the fraction of the SOL width allowed into the slot increases neutral leakage into the main chamber and increases the main-plasma density required for detachment. Preliminary modeling with the SOLPS code without drifts over-predicts the neutral pressure in detachment by a factor of 2 with the strike point in the designed operation point while more significantly over-predicts the neutral slot compression; experiments show a broader distribution of neutrals through the slot. These measurements are used to help understand detachment and validate divertor design metrics.

Distributed Hydrostatic Pressure Measurement Using Phase-OTDR in a Highly Birefringent Photonic Crystal Fiber

Abstract: Although distributed fiber-optic sensing of axial strain and temperature is a well-established technique, there are almost no demonstrations of distributed hydrostatic pressure sensing. The main obstacle for such measurements is the low sensitivity to pressure of standard optical fibers. Structured fibers, such as photonic crystal fibers, can be made pressure sensitive by means of an optimized arrangement of their internal microstructure. In this paper, we demonstrate—for the first time to our knowledge—distributed birefringence and hydrostatic pressure measurements based on phase-sensitive optical time-domain reflectometry (OTDR) in highly birefringent photonic crystal fibers. We study the response to hydrostatic pressure of two dedicated pressure-sensitive photonic crystal fibers in the range from ∼0.8 to ∼67 bar with a 5-cm spatial resolution using a phase-OTDR approach. We find differential pressure sensitivities between the slow and fast polarization axes of the studied fibers of –219 MHz/bar and 95.4 MHz/bar. These values are ∼3.8 to ∼8.8 times larger than those demonstrated previously in distributed pressure measurements with other photonic crystal fibers.

Data-driven approach for leak localization in water distribution networks using pressure sensors and spatial interpolation

Abstract: This paper presents a new data-driven method for leak localization in water distribution networks. The proposed method relies on the use of available pressure measurements in some selected internal network nodes and on the estimation of the pressure at the remaining nodes using Kriging spatial interpolation. Online leak localization is attained by comparing current pressure values with their reference values. Supported by Kriging; this comparison can be performed for all the network nodes, not only for those equipped with pressure sensors. On the one hand, reference pressure values in all nodes are obtained by applying Kriging to measurement data previously recorded under network operation without leaks. On the other hand, current pressure values at all nodes are obtained by applying Kriging to the current measured pressure values. The node that presents the maximum difference (residual) between current and reference pressure values is proposed as a leaky node candidate. Thereafter, a time horizon computation based on Bayesian reasoning is applied to consider the residual time evolution, resulting in an improved leak localization accuracy. As a data-driven approach, the proposed method does not need a hydraulic model; only historical data from normal operation is required. This is an advantage with respect to most data-driven methods that need historical data for the considered leak scenarios. Since, in practice, the obtained leak localization results will strongly depend on the number of available pressure measurements and their location, an optimal sensor placement procedure is also proposed in the paper. Three different case studies illustrate the performance of the proposed methodologies.