True Root Mean Square Research Articles

Quantitative focused laser differential interferometry with hypersonic turbulent boundary layers.

The effect of turbulent wind-tunnel-wall boundary layers on density change measurements obtained with focused laser differential interferometry (FLDI) was studied using a detailed direct numerical simulation (DNS) of the wall from the Boeing/AFOSR Mach-6 Quiet Tunnel run in its noisy configuration. The DNS was probed with an FLDI model that is capable of reading in three-dimensional time-varying density fields and computing the FLDI response. Simulated FLDI measurements smooth the boundary-layer root-mean-square (RMS) profile relative to true values obtained by directly extracting the data from the DNS. The peak of the density change RMS measured by the FLDI falls within 20% of the true density change RMS. A relationship between local spatial density change and temporal density fluctuations was determined and successfully used to estimate density fluctuations from the FLDI measurements. FLDI measurements of the freestream fluctuations are found to be dominated by the off-axis tunnel-wall boundary layers for lower frequencies despite spatial suppression provided by the technique. However, low-amplitude (0.05%-5% of the mean density) target signals placed along the tunnel centerline were successfully measured over the noise of the boundary layers (which have RMS values of about 12% of the mean). Overall, FLDI was shown to be a useful technique for making quantitative turbulence measurements and to measure finite-width sinusoidal signals through turbulent boundary layers, but may not provide enough off-focus suppression to provide accurate freestream noise measurements, particularly at lower frequencies.

Selection of C-Type Filters for Reactive Power Compensation and Filtration of Higher Harmonics Injected into the Transmission System by Arc Furnaces

This article presents a method for selecting the elements of a C-type filter working with a conventional LC-type filter for compensating reactive power and filtering out higher harmonics generated by arc furnaces and ladle furnaces. The study was conducted in a steel mill supplied by a 110 kV transmission system, where higher harmonic currents and nonlinear loads were measured. A series of computer simulations were performed under various operating conditions, and an algorithm for selecting the parameters of a third-order C-type filter (for suppressing the second harmonic) and two second-order LC-type filters (for suppressing the third harmonic) was proposed. The filtering system was tested in an arc furnace with the highest rated power, and harmonics in the current spectrum were evaluated. The results of the measurements were used to analyze the effectiveness of the compensation system comprising two passive C-type and LC-type filters at different system configurations. C-type filters significantly influenced current harmonics. The influence of the changes in the number of arc furnace transformers on the true Root Mean Square (RMS) of the currents injected into the 110 kV transmission system and on the voltages of the 110 kV busbars was discussed.

A CORDIC based Configurable Fixed-Point Design on FPGA using Minimal Hardware

Objectives: To design a COordinate Rotation DIgital Computer (CORDIC) based electrical signal processing system for efficient and minimalist electrical power processing. Methods: This stage of assessment describes the design and performance of a true RMS (Root-Mean Square) voltage meter on Xilinx SPARTAN 3E 1600 FPGA. Findings: The effectiveness of the proposed designs is assessed through FPGA implementations and error simulations. Measurement results show that the model can reproduce behaviors similar to the original model traditional use of multipliers, but with less resource consumption (hardware and processing time). Novelty: The use of CORDIC to reduce the computational cost of the algorithm, and its implementation in an embedded system.

Model of current threshold for perception in testing electrical safety performance

A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical waveforms. The relationship between human body current threshold for perception and current frequency, true root mean square (RMS) value and influence factor was described. A test system was established based on electroencephalogram (EEG) to study the relationship between human body current threshold for perception and current waveform, frequency and duty cycle so that the data could be obtained objectively and reliably. At least 850 groups of current threshold for perception and 16-lead EEGs were acquired. The theoretical analysis are verified by experimental data, and an amendment proposal on leakage current evaluation limits specified in International Electro-Technical Commission (IEC) standards is suggested.

The development and experimental validation of a numerical model of an induction skull melting furnace

Induction skull melting (ISM) is a widely used process for melting certain alloys that are very reactive in the molten condition, such as those based on Ti, TiAl, and Zr, prior to casting components such as turbine blades, engine valves, turbocharger rotors, and medical prostheses. A major research project has been undertaken with the specific target of developing improved techniques for casting TiAl components. The aims include increasing the superheat in the molten metal to allow thin section components to be cast, improving the quality of the cast components and increasing the energy efficiency of the process. As part of this, the University of Greenwich (United Kingdom) has developed a dynamic, spectral-method-based computer model of the ISM process in close collaboration with the University of Birmingham (United Kingdom), where extensive melting trials have been undertaken. This article describes in detail the numerical model that encompasses the coupled influences of turbulent flow, heat transfer with phase change, and AC and DC magneto-hydrodynamics (MHD) in a time-varying liquid metal envelope. Associated experimental measurements on Al, Ni, and TiAl alloys have been used to obtain data to validate the model. Measured data include the true root-meansquare (RMS) current applied to the induction coil, the heat transfer from the molten metal to the crucible cooling water, and the shape of the semi-levitated molten metal. Examples are given of the use of the model in optimizing the design of ISM furnaces by investigating the effects of geometric and operational parameter changes.

Power consumption measurements for ac and pulsed dc for electrostatic coalescence of water-in-oil emulsions

True root mean square power consumption measurements for coalescence of well-defined water-in-oil (W/O) emulsions [reverse osmosis water dispersed in Isopar M and stabilized with Paranox 100 surfactant] are presented for a 2-l Teflon insulated electrostatic coalescer. Estimated electricity costs for processing 1000 barrels (42 gal basis) of the emulsion were as low as $0.37 and $0.39 under 60 Hz ac and pulsed dc (i.e., half-wave rectified ac) fields, respectively. These data compare favorably with actual operating costs for an equivalent volume of crude oil for NATCO designed full-scale electrostatic coalescer systems with non-insulated electrodes. Contrary to observations by other investigators including past tests in our own laboratory, ac fields were more effective in increasing coalescence rate than pulsed dc fields. Normalized power consumption data show that the optimized frequency for coalescence with electricity costs as the important factor was at 60 Hz (i.e., the lowest frequency tested) in spite of dramatic increases in throughputs at higher frequencies of 120, 400 and 600 Hz. Comparative tests using identically prepared W/O emulsions showed that the coalescence rate with the present system was up to 11-fold higher as compared to a geometrically similar coalescer using a patented plastic-sealed electrode under identical 600 Hz ac fields.

Effect of very low pulsed direct currents at high frequency on the return of neck tension in broilers

Broiler chickens were stunned electrically for one second or 10 seconds with a unipolar pulsed direct current (DC) at 550 Hz. The effectiveness of the stun was assessed from the...

An ultrasonic system for measurement of absolute myocardial thickness using a single transducer

We have developed an ultrasonic instrument that can measure absolute regional myocardial wall motion throughout the cardiac cycle using a single epicardial piezoelectric transducer. The methods in place currently that utilize ultrasound to measure myocardial wall thickness are the transit-time sonomicrometer (TTS) and, more recently, the Doppler echo displacement method. Both methods have inherent disadvantages. To address the need for an instrument that can measure absolute dimensions of myocardial wall at any depth, an ultrasonic single-crystal sonomicrometer (SCS) system was developed. This system can identify and track the boundary of the endocardial muscle-blood interface. With this instrument, it is possible to obtain, from a single epicardial transducer, measurement of myocardial wall motion that is calibrated in absolute dimensional units. The operating principles of the proposed myocardial dimension measurement system are as follows. A short duration ultrasonic burst having a frequency of 10 MHz is transmitted from the piezoelectric transducer. Reflected echoes are sampled at two distinct time intervals to generate reference and interface sample volumes. During steady state, the two sample volumes are adjusted so that the reference volume remains entirely within the myocardium, whereas half of the interface sampled volume is located within the myocardium. After amplification and filtering, the true root mean square values of both signals are compared and an error signal is generated. A closed-loop circuit uses the integrated error signal to continuously adjust the position of the two sample volumes. We have compared our system in vitro against a known signal and in vivo against the two-crystal TTS system during control, suppression (ischemia), and enhancement (isoproterenol) of myocardial function. Results were obtained in vitro for accuracy (> 99%), signal linearity (r = 0.99), and frequency response to heart rates > 450 beats/min, and in vivo data were acquired for end-systolic dimension (r = 0.99), end-diastolic dimension (r = 0.99), and percent wall thickness (r = 0.99). Both in vitro and in vivo tests indicate that the SCS functions identically to the two-crystal TTS. Use of the SCS allows measurement of absolute wall thickness and hence myocardial function, for both acute and chronically instrumented animal studies, with minimal or no trauma to myocardium.

Dependence of the high-frequency components of the magnetoelastic voltage on plastic deformation and stress amplitude during stepwise cyclic stressing of ferromagnetic material

Abstract The high-frequency components F H of the magnetoelastic voltage u B induced during cyclic stressing of ferromagnetic material has been investigated. The true root mean square value B M of the high-frequency components was measured as a function of stress amplitude σ. The effect of strain ageing on the behaviour of B M was also studied. It was found that B M depends on the stress amplitude, plastic deformation, the dislocation arrangements and the mobility of individual dislocations. During successive stepwise increases in the stress amplitude it was found that the B M value of F H increases in the elastic and microplastic deformation range. B M reaches a maximum at a stress amplitude corresponding to the onset of the macroscopic plastic deformation Δepl. In technically pure iron the onset of the macroscopic deformation range Δepl was measured to be 0.5 × 10−4. The B M value of the high-frequency components F H decreases when the stress amplitude exceeds the value σB corresponding to the onset of ...

Preprocessing of Analog-Filter Outputs for Computer-Aided Data Acquisition

Experimental analog circuits for squaring, integrating, and taking the square root of an analog filter output have been evaluated with particular emphasis on the problems encountered with high crest-factor signals. The true root mean square value of signals having crest factors as high as 10:1 can be accurately determined, but higher (30:1) crest factors present problems because of d-c offset at the integrator input. The problem of crest factor variation with filter bandwidth can be handled by feedback from the computer used to acquire the data. The analog system is compared with a simulated digital system that samples the filter output at random time intervals, squares the amplitude, and accumulates the results. The digital approach appears to have several advantages provided that the number of samples taken is chosen to be large enough to obtain a statistically stable spectral estimate.