Results 1 - 9 of 9
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[en] This paper presents an automatic and online FDD (fault detection and diagnose) and sensor reconstruction scheme that can be used in a building energy management and control system to detect and diagnose sensor faults and reconstruct faulty sensors in building central chilling systems. The scheme is based on principal component analysis to build a model that captures the correlation among the flow meters and temperature sensors installed in the chilling systems. The model is employed to reconstruct an assumed faulty sensor. The square prediction error based on the model and the sensor validity index based on the construction are employed, respectively, to detect the sensor fault and identify the faulty sensor. An existing building central chilling system is simulated to test and validate the developed scheme online. Four types of sensor faults are introduced, respectively, during the simulation to validate the sensor FDD and sensor reconstruction scheme
[en] A novel mode-locked Nd:YAG oscillator has been developed by using an ultrafast photoconductive feedback controlled loop, and mode-locked pulses with a duration of 100ps have been obtained. The energy instability of the pulse trains is ±5%. In this type of mode-locking technology, a type of deep-level doped GaAs (Cr-doped) photoconductive switch, which has a fast response in time and is free of avalance process, is used to drive a Pockels' cell to realize mode-locking. The dark resistance of this type of photoconductive switch is 6 orders of magnitude higher than that of the intrinsic single-crystal silicon, and it can reach a level as high as 109 ohms. Consequently, it is able to withstand longterm operation at several thousand DC volts. By means of the photoconductive ohmic switch characteristics, the authors have designed a positive feedback control network which has a very fast response time, and can couple a voltage of up to a thousand volts. Using this unit in a Nd:YAG laser, they have successfully realized a very stable mode-locked pulse train with pulse width shorter than 100 ps. The operation principle, and the results of the preliminary experiments are presented here. 1 ref., 3 figs
[en] A method of fault detection, diagnosis (FDD) and data recovery is proposed for building heating/cooling billing system in this paper. Principal component analysis (PCA) approach is used to extract the correlation of measured variables in heating/cooling billing system and reduce the dimension of measured data. The measured data of billing system under normal operating condition are used to build PCA model. Sensor faults of bias, drifting and complete failure are introduced to building heating/cooling billing system for detection and identification. Square prediction error (SPE) statistic is used to detect sensor faults in the system. Then, sensor validity index (SVI) was employed to identify faulty sensors. Finally, a reconstruction algorithm is presented to recover the correct data of faulty sensor in accordance with the correlations among system variables. A program for the FDD and data recovery method is developed and employed in the heating/cooling billing system of a real small-scale laboratory building to test its applicability and effectiveness. Validation results show that the proposed FDD and data recovery method is correct and effective for most faults in building heating/cooling billing system.
[en] Graphite flake/Cu composites with Cu or TiC coatings on the graphite surface were fabricated via a powder metallurgy method. The effect of the flake’s surface coating on the microstructure and thermal conductivities of the graphite flake/Cu composites was studied. The results show that a good contact interfacial structure is established when the TiC or Cu coating is introduced. The thermal conductivity of the TiC- and Cu-coated composites with a 60 vol% flake reached 668 W m−1 K−1 and 612 W m−1 K−1, respectively. A modified Diffuse Mismatch Model for anisotropic graphite was established to estimate the interfacial thermal resistance, and the Effective Medium Approach was used to analyze the thermal conductivity behavior of composites. The results show that both coated composites exhibit low interfacial thermal resistance, resulting in high thermal conductivity in the X-Y plane. The thermal conductivity may be further enhanced if a preferable alignment control is used. (paper)
[en] This work describes the microstructure and mechanical properties of B-C-N-H films synthesized by medium frequency magnetron sputtering from a boron target in a N2 + CH4 + Ar gas mixture. The increase in the CH4 flow rate increases the carbonaceous compound species, causes the increase of the C atomic concentration and promotes the formation of sp3-hybridized carbon. The change of hardness with the CH4 flow rate had a relationship with the residual stress. The coefficient of friction was reduced approximately from 0.8 to 0.18, and wear resistance was considerably improved by increasing the flow of CH4 gas component from 0 to 40 sccm. The change of films' hardness was discussed and attributed primarily to the internal defects and bonding characteristics, while the superior tribological properties of the films could be assigned to the formation of sp3-hybridized carbon and the C-H bonding.
[en] Al-containing hydrogenated amorphous carbon (Al-C : H) films were deposited on silicon substrates using a mid frequency magnetron sputtering Al target in an argon and methane gas mixture. The composition, surface morphology, hardness and friction coefficient of the films were characterized using x-ray photoelectron spectroscopy, atomic force microscopy, nanoindentation and tribological tester. The Al-C : H films deposited at low CH4 content show high surface roughness, low hardness and high friction coefficient, similar to metallic Al films; in contrast, the Al-C : H films prepared under high CH4 content indicate low surface roughness, high hardness and low friction coefficient, close to that of hard a-C : H films as wear-resistance films
[en] This paper presents an approach to isolate flow meter faults in building central chilling systems. It mathematically explains the fault collinearity among the flow meters in central chilling systems and points out that the sensor validation index (SVI) used in principal component analysis (PCA) is incapable of isolating flow meter faults due to the fault collinearity. The wavelet transform is used to isolate the flow meter faults as a substitute for the SVI of PCA. This approach can identify various variations in measuring signals, such as ramp, step, discontinuity etc., due to the good property of the wavelet in local time-frequency. Some examples are given to demonstrate its ability of fault isolation for the flow meters
[en] Ti-doped hydrogenated diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates by a filtered cathodic vacuum arc (FCVA) method using Ar and CH4 as the feedstock. The composition and microstructure of the films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and IR spectroscopy. The internal stress was determined by the radius of curvature technique. The influence of the bias voltage on the microstructure of the as-deposited films was investigated. It was found that the graphite-like bonds was dominated in the Ti-doped DLC film deposited at 0 V bias voltage. When bias voltage was increased to -150 V, more diamond-like bond were produced and the sp3 content in film reached the maximum value, after which it decreased and more graphite-like bonds feature produced with further increase of the negative bias voltage. The compressive internal in the Ti-doped DLC films also exhibited a maximum value at -150 V bias voltage. IR results indicated that C-H bonded intensity reduced, and H atoms bonded with C atoms were substituted for the Ti atoms as the negative bias voltage increasing. All the composition and microstructure change can be explained by considering the plasma conditions and the effect of negative bias voltage applied to the substrate