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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.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Sea-level evaluation of digitally implemented turbojet engine control functions

The standard hydromechanical control system of a turbojet engine was replaced with a digital control system that implemented the same control laws. A detailed discussion of the digital control system in use with the engine is presented. The engine was operated in a sea-level test stand. The effects of control update interval are defined, and a method for extending this interval by using digital compensation is discussed.

Arpasi, D. J.↗
NASA NTRS1971

Digital magnetic temperature transducer.

A new digital magnetic temperature transducer is reported. The device utilizes the discontinuous behavior of the initial permeability with temperature at the Curie temperature of some magnetic materials. Since the Curie temperature is determined by the chemical and crystallographic composition of the particular material only, the transducer requires no calibration and has extremely high stability and reproducibility with time. The output of the transducer is inherently digital and, therefore, is directly compatible with the digital information processing and control without A/D conversion. The temperature-sensing portion of the transducer consists only of magnetic cores and wire and, therefore, has extremely high reliability, is shock and radiation insensitive, small, and virtually indestructible.

Tchernev, D. I.↗
NASA NTRS1972

Digital autopilot for the SKYLAB orbital assembly.

In Project SKYLAB, the Command and Service Module which ferries astronaut crews to and from the Orbital Workshop is required to have the capability of providing attitude control for the entire Orbital Assembly during docked phases of the mission. A digital autopilot has been designed which meets this requirement. It is a direct descendant of the digital autopilot designed for and used extensively in project Apollo. There is a major difference however. For Apollo, it was reasonable to design an autopilot that treated the roll, pitch, and yaw axes independently. Because of the geometry of the Orbital Assembly, however, it is of considerable advantage to design the jet selection logic for SKYLAB such that the roll and pitch axes are treated as coupled, and also that the roll and yaw axes are treated as coupled. This paper discusses how inter-axis dependence has been incorporated in the Command and Service Module's digital autopilot while working within the limitations of the onboard computer.

Turnbull, J. F.↗
NASA NTRS1972

An all digital phase locked loop for FM demodulation.

A phase-locked loop designed with all-digital circuitry which avoids certain problems, and a digital voltage controlled oscillator algorithm are described. The system operates synchronously and performs all required digital calculations within one sampling period, thereby performing as a real-time special-purpose computer. The SNR ratio is computed for frequency offsets and sinusoidal modulation, and experimental results verify the theoretical calculations.

Greco, J.↗
NASA NTRS1972

Time-domain technique for optimal design of digital-filter equalizers.

A technique is presented for the design of frequency-sampling and transversal digital filters from specified unit-impulse responses. The multiplier coefficients for the digital filter are specified by the use of a linear-programming algorithm. Examples include the design of digital filters to generate intersymbol-free pulses for data transmission over ideal bandlimited channels and to equalize data transmission channels that have known unit-impulse responses.

Burlage, D. W.↗
NASA NTRS1972

Automatic N(h,t) profiles of the ionosphere with a digital ionosonde

A method is described to accomplish automatic data selection and profile inversion to obtain ionospheric electron density profiles from digitized radio soundings. The profile inversion is based on a well-established formulation by which the optimum radio frequency sounding intervals can be specified from an approximate knowledge of the profile; the expected virtual height coordinates (h) at these frequencies (f) are estimated, and procedures are then used to select h(f) observations nearest the predicted coordinates from a subsequent digital ionogram. From these the next profile is obtained. The process adaptively follows the changing shape and detail of the profile. The procedure requires an average of 15 sec per profile on a standard data processing computer, and can be adapted, with benefit to online real-time use in a digital ionosonde.

Wright, J. W.↗
NASA NTRS1972

Fast digital noise filter capable of locating spectral peaks and shoulders

Experimental data frequently have a poor signal-to-noise ratio which one would like to enhance before analysis. With the data in digital form, this may be accomplished by means of a digital filter. A fast digital filter based upon the principle of least squares and using the techniques of convoluting integers is described. In addition to smoothing, this filter also is capable of accurately and simultaneously locating spectral peaks and shoulders. This technique has been adapted into a computer subroutine, and results of several test cases are shown, including mass spectral data and data from a proportional counter for the High Energy Astronomy Observatory.

Edwards, T. R.↗
NASA NTRS1972

A proposed magnetic digital temperature transducer, volume 1

A study has been made of the feasibility of using the discontinuous permeability versus temperature characteristics of some magnetic materials for a digital temperature transducer and a thermally controlled ON-OFF switch. Simple logic converts the number of output pulse to a digital word recognizable by the system. Efforts have been concentrated on materials with Curie temperatures between 0 and 100 C. One compound has the composition Mn(5-x)Fe(x)Ge3 where the amount of iron determines the transition temperature. The other compound is Ni-Zn ferrite and has the compositon Ni(1-x)Zn(x)Fe(1.95)O4 where the nickel: zinc ratio determines the transition temperature. A detailed report of materials prepared is presented. Toroidal inductors of the material have been constructed and the change in inductance with temperature measured. In view of these initial measurements, it is felt that a transducer utilizing the permeability versus temperature characteristics of these materials has promise as a reliable and sensitive solid state digital temperature transducer.

Collier, T. E.↗
NASA NTRS1972

A TDM link with channel coding and digital voice.

The features of a TDM (time-division multiplexed) link model are described. A PCM telemetry sequence was coded for error correction and multiplexed with a digitized voice channel. An all-digital implementation of a variable-slope delta modulation algorithm was used to digitize the voice channel. The results of extensive testing are reported. The measured coding gain and the system performance over a Gaussian channel are compared with theoretical predictions and computer simulations. Word intelligibility scores are reported as a measure of voice channel performance.

Jones, M. W.↗
NASA NTRS1973

Digital single-sideband modulation.

This paper considers digitized Weaver modulators for single-sideband modulation that can be used in radio communications and telemetering. A system of 12 such modulators to process 12 analog signals digitally is replaced by six multiplex modulators at the cost of additional computation at the input but with an overall reduction in computation time and a higher degree of accuracy. A unique digital filter is developed that can interpolate and output samples at multiples of the input sampling rate and exhibits a passband that occurs above the Nyquist frequency with no apparent distortion effects. A discussion of the Fortran simulation of a combined modulator-demodulator structure is included to verify the effectiveness of this scheme.

Singh, S.↗
NASA NTRS1973

Microprogrammed digital filters for strapdown guidance application.

Discussion of an approach for implementing digital filters using microprogrammed control logic with read only memory (ROM) for strapdown guidance applications, and description of a second-order multiplexed system using multiprogrammed control instruction. The microprogramming technique for control using ROM is shown to enhance higher order digital filter realization. The high speed of digital circuits reduces propagation time and facilitates multiplexing. Programmed ROM's can be altered easily for different algorithms.

Kapadia, K.↗
NASA NTRS1973

On the design of wave digital filters with low sensitivity properties.

The wave digital filter patterned after doubly terminated maximum available power (MAP) networks by means of the Richard's transformation has been shown to have low-coefficient-sensitivity properties. This paper examines the exact nature of the relationship between the wave-digital-filter structure and the MAP networks and how the sensitivity property arises, which permits implementation of the digital structure with a lower coefficient word length than that possible with the conventional structures. The proper design procedure is specified and the nature of the unique complementary outputs is discussed. Finally, an example is considered which illustrates the design, the conversion techniques, and the low sensitivity properties.

Renner, K.↗
NASA NTRS1974

Decimal digit generator for commutated data: A Concept

Perform analog-to-digital conversion on input signal with staircase circuit having 10% resolution, convert digital result to analog voltage, subtract it from original input signal; read out feedback signals as decimal digit representation during one clock phase and servo-error difference between input and feedback as analog portion during following clock phase.

Rusk, S. J.↗
NASA NTRS1974

Anti-multipath digital signal detector

Detector operates in conjunction with radio frequency portion of receiver to detect digital signals transmitted in known modulation formats. Signal is constructed by assigning known and distinct modulation waveforms to sequence of message symbols. It reconstructs transmitted digital sequence with minimum probability that any reconstructed digit will be in error.

Painter, J. H.↗
NASA NTRS1973

Technique for extending the frequency range of digital dividers

A technique for extending the frequency range of a presettable digital divider is described. The conventional digital divider consists of several counter stages with the count of each stage compared to a preselected number. When the counts for all stages are equal to the preselected numbers, an output pulse is generated and all stages are reset. For high input frequencies, the least significant stage of the divider has to be reset in a very short time. This limits the frequency that can be handled by the conventional digital divider. This invention provides a technique in which the second least significant and higher stages are reset and the least significant stage is permitted to free-run. Hence, the time in which the reset operation can be performed is increased thereby extending the frequency range of the divider.

Long, W. C.↗
NASA NTRS1974

Digital controller for a Baum folding machine

A digital controller for controlling the operation of a folding machine enables automatic folding of a desired number of sheets responsive to entry of that number into a selector. The controller includes three decade counter stages for corresponding rows of units, tens and hundreds push buttons. Each stage including a decimal-to-BCD encoder, a buffer register, and a digital or binary counter. The BCD representation of the selected count for each digit is loaded into the respective decade down counters. Pulses generated by a sensor and associated circuitry are used to decrease the count in the decade counters. When the content of the decade counter reaches either 0 or 1, a solenoid control valve is actuated which interrupts operation of the machine. A repeat switch, when actuated, prevents clearing of the buffer registers so that multiple groups of the same number of sheets can be folded without reentering the number into the selector.

Bryant, W. H.↗
NASA NTRS1974

Computer-implemented land use classification with pattern recognition software and ERTS digital data

Significant progress has been made in the classification of surface conditions (land uses) with computer-implemented techniques based on the use of ERTS digital data and pattern recognition software. The supervised technique presently used at the NASA Earth Resources Laboratory is based on maximum likelihood ratioing with a digital table look-up approach to classification. After classification, colors are assigned to the various surface conditions (land uses) classified, and the color-coded classification is film recorded on either positive or negative 9 1/2 in. film at the scale desired. Prints of the film strips are then mosaicked and photographed to produce a land use map in the format desired. Computer extraction of statistical information is performed to show the extent of each surface condition (land use) within any given land unit that can be identified in the image. Evaluations of the product indicate that classification accuracy is well within the limits for use by land resource managers and administrators. Classifications performed with digital data acquired during different seasons indicate that the combination of two or more classifications offer even better accuracy.

Joyce, A. T.↗
NASA NTRS1974

Digital servo control of random sound test excitation

A digital servocontrol system for random noise excitation of a test object in a reverberant acoustic chamber employs a plurality of sensors spaced in the sound field to produce signals in separate channels which are decorrelated and averaged. The average signal is divided into a plurality of adjacent frequency bands cyclically sampled by a time division multiplex system, converted into digital form, and compared to a predetermined spectrum value stored in digital form. The results of the comparisons are used to control a time-shared up-down counter to develop gain control signals for the respective frequency bands in the spectrum of random sound energy picked up by the microphones.

Nakich, R. B.↗