Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “frequency measurement”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Apparatuses and methods for testing electrochemical cells by measuring frequency response

Real-time battery impedance spectra are acquired by stimulating a battery or battery system with a signal generated as a sum of sine signals at related frequencies. An impedance measurement device can be used to interface between the battery system and a host computer for generating the signals. The impedance measurement device may be calibrated to adapt the response signal to more closely match other impedance measurement techniques. The impedance measurement device may be adapted to operate at mid-range voltages of about 50 volts and high-range voltages up to about 300 volts.

Christophersen, Jon P.↗
NASA NTRS1991

Line-frequency measurements and analysis of N2O between 900 and 4700/cm

The N2O infrared spectrum from 900 to 4700/cm has been studied with a high-resolution Fourier-transform spectrometer. Measurements were made of line frequencies of several N2O isotopes for several ground-state and hot bands. These bands include the 1530-0330, 2330-0330, 0441-0440, 0441-0330, 0531-0330, and 1331-0330 bands of (N-14)2(O-16). Also, perturbation-enhanced transitions in the 0710-0110 and 0730-0110 bands were assigned and measured. The frequencies have been analyzed to obtain a unique set of effective vibration-rotation parameters for each vibrational state. The results obtained from this research are of high accuracy for the ground-state, and the first-excited-state bands of (N-14)2(O-16), in which the computed frequencies derived from the least-squares fits, are known to an absolute uncertainty of only +/-4 x 10 exp -5 for nonperturbed transitions.

Toth, Robert A.↗
NASA NTRS1978

A modular multiple use system for precise time and frequency measurement and distribution

A modular CAMAC based system is described which was developed to meet a variety of precise time and frequency measurement and distribution needs. The system was based on a generalization of the dual mixer concept. By using a 16 channel 100 ns event clock, the system can intercompare the phase of 16 frequency standards with subpicosecond resolution. The system has a noise floor of 26 fs and a long term stability on the order of 1 ps or better. The system also used a digitally controlled crystal oscillator in a control loop to provide an offsettable 5 MHz output with subpicosecond phase tracking capability. A detailed description of the system is given including theory of operation and performance. A method to improve the performance of the dual mixer technique is discussed when phase balancing of the two input ports cannot be accomplished.

Reinhardt, V. S.↗
DOE OSTI2024

CROCUS High-Frequency Measurements of CO₂, H₂O, Wind, and Temperature at University of Illinois Chicago

As of April 9, 2026: this dataset is currently being versioned to include data up to March 31, 2026. Once the versioning process is complete, new data files will be available for access. The dataset metadata will also be updated to reflect the data availability of the new data being versioned. Raw atmospheric measurements collected at the University of Illinois Chicago (UIC) as part of the Community Research on Climate and Urban Science (CROCUS) project. The data includes high-frequency measurements of carbon dioxide (CO₂) concentration, water vapor (H₂O) concentration, wind speed (U, V, W components), temperature, and atmospheric pressure. These raw data are recorded by the LI-7500DS Open Path CO₂/H₂O Analyzer and a sonic anemometer at a 10 Hz acquisition frequency, providing the necessary inputs for calculating fluxes of CO₂, H₂O, heat, and momentum. In addition to gas concentration measurements, the dataset includes diagnostic information from the instruments, including absorptance, sample and reference signals, and diagnostic values. The data were collected to study urban atmospheric conditions and contribute to flux calculations for urban climate research. These measurements form the basis for calculating 30-minute average fluxes of key atmospheric variables using the eddy covariance method. This dataset provides critical raw input data for researchers interested in atmospheric fluxes, urban air quality, and the interaction between the urban environment and atmospheric processes. The data is part of the U.S. Department of Energy’s Biological and Environmental Research (BER) program, under the CROCUS Urban Integrated Field Laboratory (UIFL) project.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1989

Apparatus for using a time interval counter to measure frequency stability

An apparatus for measuring the relative stability of two signals is disclosed comprising a means for mixing the two signals down to a beat note sine wave and for producing a beat note square wave whose upcrossings are the same as the sine wave. A source of reference frequency is supplied to a clock divider and interval counter to synchronize them and to generate a picket fence for providing a time reference grid of period shorter than the beat period. An interval counter is employed to make a preliminary measurement between successive upcrossings of the beat note square wave for providing an approximate time interval therebetween as a reference. The beat note square wave and the picket fence are then provided to the interval counter to provide an output consisting of the time difference between the upcrossing of each beat note square wave cycle and the next picket fence pulse such that the counter is ready for each upcrossing and dead time is avoided. A computer containing an algorithm for calculating the exact times of the beat note upcrossings then computes the upcrossing times.

Greenhall, Charles A.↗
NASA NTRS1990

Time and frequency measuring metrological equipment in the USSR

The complex of the means of providing time and frequency traceability in the USSR includes the system of time and frequency standards of the National Time and Frequency Calibration Service, time and frequency transfer facilities and local time and frequency standards. Control on measurement correctness is performed by the All-Union State Standard calibration service. The hardware of most of the above-mentioned systems is provided by the instruments developed by our institute. A common scientific and technological approach allowed us to create a unified system of time-frequency equipment composed of widely used serial instruments, sets, automated systems and complexes. Primary frequency standards of different classes, time and frequency references and instruments are based on the unified system. CH1-70 hydrogen frequency standard and its CH1-70A, CH1-80 modifications are used in the group time and frequency standards. Measuring time and data processing techniques, and also instrumentation specifications on the results of 10-year operation are given. The existing system provides time-frequency measurements with 2 times 10(exp -13) plus or minus 1 times 10(exp -14) accuracy.

Uljanov, Adolph A.↗
NASA NTRS1994

Pressure broadening of ClO by N2 and O2 near 204 and 649 GHz and new frequency measurements between 632 and 725 GHz

The N2 and O2 pressure broadening of the ClO transitions near 204 and 649 GHz have been measured between 200 and 300 K. Oxygen broadening has been measured for the transitions near 278 GHz. The accuracy of the derived air broadening is comparable to that for the air broadening of stable species and is estimated to be within approximately 3% over the entire temperature range. These transitions are currently being used for satellite, balloon, and ground based monitoring of atmospheric ClO, respectively. Some new frequency measurements are reported in the 632 - 725 GHz range. These are in good agreement with previous measurements and predictions.

Oh, J. J.↗
DOE OSTI2024

Fault-tolerant grid frequency measurement algorithm during transients

A system determines the frequency of grid signals corresponding to an electrical grid in real time. The system includes a transient detector that monitors a grid signal from a voltage meter or a current meter connected to the electrical grid. The system produces, in real time and at a sampling rate, a deviation signal indicative of a periodicity of the monitored grid signal. The system determines, over one or more cycles of the monitored grid signal, a measurement signal corresponding to the deviation signal. The system determines a frequency signal that corresponds a frequency estimation of the monitored signal by applying a frequency estimation when values of the measurement signal are less than a deviation threshold and maintaining the frequency signal at a constant value when values of the measured signal equal or exceeds the deviation threshold.

Zhan, Lingwei↗
NASA NTRS1972

Convergence of oscillator spectral estimators for counted-frequency measurements.

A common intermediary connecting frequency-noise calibration or testing of an oscillator to useful applications is the spectral density of the frequency-deviating process. In attempting to turn test data into predicts of performance characteristics, one is naturally led to estimation of statistical values by sample-mean and sample-variance techniques. However, sample means and sample variances themselves are statistical quantities that do not necessarily converge (in the mean-square sense) to actual ensemble-average means and variances, except perhaps for excessively large sample sizes. This is especially true for the flicker noise component of oscillators. This article shows, for the various types of noises found in oscillators, how sample averages converge (or do not converge) to their statistical counterparts. The convergence rate is shown to be the same for all oscillators of a given spectral type.

Tausworthe, R. C.↗
DOE OSTI2021

Open Source Fault-tolerant Grid Frequency Measurement for Solar Inverters

The Discrete Fourier transform (DFT) based measurement algorithms are one of the most common measurement algorithms for grid parameter estimation such as rms, phase angle, frequency. Over the past few years, many DFT based algorithms have been developed to enhance its measurement accuracy under steady-state and/or dynamic grid conditions. For example, an adaptive band-pass filter utilizing exponential modulation filter has been proposed to reduce measurement errors at the presence of large frequency deviations. Measurement accuracy of different algorithms including FIR filter, extended Kalman filtering (EKF), and enhanced DFT method have been compared in detail under different grid conditions. Two artificial signals that have 90-degree phase difference were constructed by the Clarke transformation to address the frequency spectrum leakage of DFT. A multi-module approach was developed to enhance both steady-state and dynamic measurement accuracies, in which each module was developed to eliminate some specific errors. Besides DFT-based measurement algorithms, some signal model-based algorithms have been developed to further improve the accuracy under dynamic conditions. However, a key drawback of the state-of-the-art algorithms is that they cannot perform measurements accurately during system transient faults. In the Blue Cut Fire event, there was a phase angle jump of about 26 degrees in the voltage waveform during the transient fault. The phase angle jump fault will cause waveform discontinuity, and these algorithms will fail to provide reliable measurements during this period because they typically assume the waveform to be measured is continuous, no matter what method (DFT, PLL, EKF, FIR, or Taylor WLS) is used for estimation. In fact, the measurement errors during the system transient faults like phase-jump is not required in the IEEE Standard. As a result, although a measurement instrument can pass the strict IEEE Standard, it could still be the source of the problem in the future if we have similar system transient faults, which could happen again. Therefore, developing the fault-tolerant measurement technology is the key to solve the problem.

14 SOLAR ENERGY↗
NASA NTRS1977

Absorption of sound in air - High-frequency measurements

The absorption of sound in air at frequencies from 4 to 100 kHz in 1/12 octave intervals, for temperatures from 255.4 K (0 F) to 310.9 K (100 F) in 5.5 K (10 F) intervals, and at 10% relative-humidity increments between 0% and saturation has been measured. The values of free-field absorption have been analyzed to determine the relaxation frequency of oxygen for each of the 92 combinations of temperature and relative humidity studied and the results are compared to an empirical expression. The relaxation frequencies of oxygen have been analyzed to determine the microscopic energy-transfer rates.

Bass, H. E.↗