Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “multiplexing”

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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

1.0 to 2.5 micrometer short wavelength infrared /SWIR/ linear array technology for low background applications

A design concept is presented for a hybrid linear focal plane array operating in the 1.0 to 2.5 micron band under low background conditions such as encountered in spaceborne missions. The concept is based on direct gate coupling of the input from a photovoltaic mercury-cadmium telluride detector into a CCD multiplexer. Theoretical analysis indicates a specific detectivity at peak wavelength on the order of 10 to the 12th cm sq rt Hz/W when the system is operating at 200 K. Values of the voltage responsivity, specific detectivity and the relative voltage noise levels of the coupled system obtained in experimental studies with direct-gate-coupled 4.0-micron detectors support the theoretical analysis performed for the case of system detectivity limited by the CCD 1/f noise.

Stobie, J.↗
NASA NTRS1982

Integrating 128-element linear imager for the 1 to 5 microns region

Useful charge integration has been achieved in high quality photovoltaic InSb diodes when combined with a FET multiplexing (MUX) scheme. An experimental detector assembly with a linear array of 128 InSb diodes coupled to a FEX MUX has been developed. The first stage J-FET preamp, pixel reset switch, MUX, and the InSb array are contained in a hybrid microcircuit of compact dimensions. A low noise preamplifier topology which capitalizes on the low video line capacitance inherent with hybrid fabrication techniques is also utilized. Measurements indicate a signal-to-noise ratio of over 1000:1 and response uniformity of + or - 2 percent. Sample images show subtle detail which supports the estimated radiometric sensitivity of 0.01 K.

Bailey, G. C.↗
NASA NTRS1982

Development and evaluation of integrated infrared arrays for astronomical applications

The status of a technology program to evaluate existing infrared detector arrays, and to develop improved ones for low background astronomical applications, is described. For applications such as the Shuttle Infrared Telescope Facility, arrays that cover as much of the 1-1000 micron range as possible are of interest. Low background test results for a 2 x 64 Si:Bi charge-injection-device, and 1 x 20 InSb charge-coupled-device arrays, are included. As a result of the present testing, improved, astronomy-optimized extrinsic silicon arrays in both linear and area formats are planned. Efforts to develop accumulation mode MOSFETs specifically for liquid helium temperatures, and cryogenic amplifier and multiplexer circuits, are discussed.

Mccreight, C. R.↗
NASA NTRS1982

Near-infrared linear array spectrometer for space applications

A 128-element InSb linear detector array read out with a field effect transistor (FET) multiplexing scheme has been developed at the Jet Propulsion Laboratory. State-of-the-art NEP, uniform response, on-detector charge integration, and very low focal plane heat load compared to that of discrete detector arrays allows this type of array to open new possibilities for spaceborne near-infrared imaging spectrometers. Large number of cooled detector elements are feasible with the new technology, making it practical to design sensitive spectrometers even for spinning spacecraft where simultaneous wavelength coverage is necessary to avoid confusion of spatial with spectral variations.

Apt, J.↗
NASA NTRS1983

An ultraviolet spectrograph using an echelle grating with cross-disperser for the measurement of stratospheric constituents

The present investigation is concerned with the development of a high resolution echelle-cross disperser grating spectrograph for application in groundbased, balloon, and Shuttle studies of the middle atmosphere and thermosphere. All the design features discussed pertain specifically to the balloon instrument. Attention is given to examples of scientific objectives for the middle atmosphere, aspects of instrument description, imaging requirements, the spectral multiplexing capability, broad wavelength coverage, sensitivity, dynamic range, scattered light, the optical configuration of the instrument, the detector system, the data system, and the results of laboratory tests and theoretical evaluations.

Torr, D. G.↗
NASA NTRS1983

Triangular system solutions on an optical systolic processor

It is noted that the simplified system of equations presented by Casasent and Ghosh (1983) can also be solved optically. One realization of this is described, with attention given to data flow and speed for the case of a lower triangular system of equations. The solution of an upper triangular system of equations can be handled in analogous fashion. The problem requires a matrix-vector processor. Only one carrier frequency input to the acoustooptic cell and only one output detector are used. To multiply a matrix by a vector in this system, the time-multiplexed vector elements are fed into the acoustooptic cell.

Ghosh, A.↗
NASA NTRS1983

Design and performance of the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument

Design and performance data are analyzed for the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument, which has been developed for the NASA Earth Radiation Budget Satellite (ERBS). SAGE II is designed to monitor globally, from 70 degrees S to 70 degrees N latitude, the vertical distribution of stratospheric aerosols, ozone, water vapor, and nitrogen dioxide by measuring the extinction of solar radiation through the earth's atmosphere during the ERBS observatory solar occultations. A flat scanning mirror reflects solar radiation into a Cassegrain type telescope, which forms a solar image on the entrance slit of a grating spectrometer. The instantaneous-field-of-view of the SAGE II is scanned along the vertical solar diameter by the elevation scan mirror. The optical system is contained within an azimuth gimbal which tracks the solar radiometric centroid during the data event, while the spectrometer isolates seven spectral wavelengths from 0.385-1.02 micrometers. The seven channels of the spectrometer use silicon photodiode dedectors operated in the photovoltaic mode. The detector outputs are multiplexed into a serial data stream for readout by the ERBS telemetry system, with each output being sampled 64 times per second and digitized to 12 bit resolution.

Zaun, N. H.↗
NASA NTRS1982

Comparison of channel assignment techniques for hybrid switching

The performance of four circuit-switched channel assignment strategies for use in a hybrid switch accommodating multiple users is analyzed and compared. Each scheme is associated with a fixed frame movable boundary TDM channel that multiplexes circuit-switched (CS) and packet-switched (PS) traffic. The performance measures used are blocking probability for the circuit-switched traffic and time delay for the packet-switched traffic.

Schwartz, M.↗
NASA NTRS1982

Instrumentation, data acquisition and reduction for a large spaceborne helium dewar

The data acquisition system monitors five types of transducers: (1) platinum and germanium resistance thermometers; (2) superconducting liquid level indicators for both cryogen tanks; (3) pressure transducers for both tanks; (4) strain gauges at critical structural locations; and (5) flowmeters for monitoring cryogen tank boiloff which are linear voltage output transducers. All the transducers produce a voltage proportional to the parameter they measure; this is routed to a single six and one-half digit voltmeter by way of an 80-channel multiplexer. The data acquisition program has six main functions: (1) definition and modification of the channels to be stimulated; (2) sensor stimulation and measurement; (3) raw data storage; (4) raw data conversion; (5) real-time formatting and output of raw or converted data; and (6) editing. The heart of the program is a driver section that represents approximately 20 percent of the code. The driver mode sequences and controls the six main functions.

Brooks, W. F.↗
NASA NTRS1983

LU and Cholesky decomposition on an optical systolic array processor

Direct solutions of matrix-vector equations on an optical systolic array processor are considered. The solutions are discussed and a parallel algorithm for LU matrix decomposition that is very attractive for an optical realization is formulated. It is noted that when direct techniques are used, it is preferable to realize the matrix decomposition on an optical system and to utilize a digital processor for the solution of the simplified resultant matrix-vector problem. One method of realizing LU matrix decomposition on a new frequency-multiplexed optical systolic array matrix-matrix processor is described. A simple method for extending the process of LU decomposition to Cholesky decomposition on the optical processor is discussed.

Casasent, D.↗
NASA NTRS1985

Capacitor-Test System

Polycarbonate film capacitors tested for leakage paths with microprocessor controlled multiplexer test sequence. Microprocessor based capacitor test system simultaneously monitors 80 capacitors.

Ott, F. M.↗
NASA NTRS1983

High energy efficient solid state laser sources

Slab glass performance studies demonstate 18 J of output at 2 Hz with 2.3% wall plug efficiency. The goal is to achieve 10 J per pulse at 10 Hz and 3% wall plug efficiency during the next annual period. The slab concept was extended to Nd:YAG and to Nd:GGG. To date over 80 W of CW output power at 2% efficiency was generated in slab Nd:YAG. A multiplexed slab Nd:YAG pre-amplifier was invented and a Nd:YAG oscillator was demonstrated with 100kHz linewidth for eventual use in wind velocity measurements.

Byer, R. L.↗
NASA NTRS1983

Self-correcting electronically scanned pressure sensor

A multiple channel high data rate pressure sensing device is disclosed for use in wind tunnels, spacecraft, airborne, process control, automotive, etc., pressure measurements. Data rates in excess of 100,000 measurements per second are offered with inaccuracies from temperature shifts less than 0.25% (nominal) of full scale over a temperature span of 55 C. The device consists of thirty-two solid state sensors, signal multiplexing electronics to electronically address each sensor, and digital electronic circuitry to automatically correct the inherent thermal shift errors of the pressure sensors and their associated electronics.

Gross, C.↗
NASA NTRS1983

Spacelab Data Processing Facility

The Spacelab Data Processing Facility (SDPF) processes, monitors, and accounts for the payload data from Spacelab and other Shuttle missions and forwards relevant data to various user facilities worldwide. The SLDPF is divided into the Spacelab Input Processing System (SIPS) and the Spacelab Output Processing System (SOPS). The SIPS division demultiplexes, synchronizes, time tags, quality checks, accounts for the data, and formats the data onto tapes. The SOPS division further edits, blocks, formats, and records the data on tape for shipment to users. User experiments must conform to the Spacelab's onboard High Rate Multiplexer (HRM) format for maximum process ability. Audio, analog, instrumentation, high density, experiment data, input/output data, quality control and accounting, and experimental channel tapes along with a variety of spacelab ancillary tapes are provided to the user by SLDPF.

Source record↗
NASA NTRS1984

Real time pressure signal system for a rotary engine

A real-time IMEP signal which is a composite of those produced in any one chamber of a three-lobed rotary engine is developed by processing the signals of four transducers positioned in a Wankel engine housing such that the rotor overlaps two of the transducers for a brief period during each cycle. During the overlap period of any two transducers, their output is compared and sampled for 10 microseconds per 0.18 degree of rotation by a sampling switch and capacitive circuit. When the switch is closed, the instantaneous difference between the value of the transducer signals is provided while with the switch open the average difference is produced. This combined signal, along with the original signal of the second transducer, is fed through a multiplexer to a pressure output terminal. Timing circuits, controlled by a crank angle encoder on the engine, determine which compared transducer signals are applied to the output terminal and when, as well as the open and closed periods of the switches.

Rice, W. J.↗
NASA NTRS1984

An improved dual-frequency technique for the remote sensing of ocean currents and wave spectra

A two frequency microwave radar technique for the remote sensing of directional ocean wave spectra and surface currents is investigated. This technique is conceptually attractive because its operational physical principle involves a spatial electromagnetic scattering resonance with a single, but selectable, long gravity wave. Multiplexing of signals having different spacing of the two transmitted frequencies allows measurements of the entire long wave ocean spectrum to be carried out. A new scatterometer is developed and experimentally tested which is capable of making measurements having much larger signal/background values than previously possible. This instrument couples the resonance technique with coherent, frequency agility radar capabilities. This scatterometer is presently configured for supporting a program of surface current measurements.

Schuler, D. L.↗
NASA NTRS1983

Low-frequency radio navigation system

A method of continuous wave navigation using four transmitters operating at sufficiently low frequencies to assure essentially pure groundwave operation is described. The transmitters are keyed to transmit constant bursts (1/4 sec) in a time-multiplexed pattern with phase modulation of at least one transmitter for identification of the transmitters and with the ability to identify the absolute phase of the modulated transmitter and the ability to modulate low rate data for transmission. The transmitters are optimally positioned to provide groundwave coverage over a service region of about 50 by 50 km for the frequencies selected in the range of 200 to 500 kHz, but their locations are not critical because of the beneficial effect of overdetermination of position of a receiver made possible by the fourth transmitter. Four frequencies are used, at least two of which are selected to provide optimal resolution. All transmitters are synchronized to an average phase as received by a monitor receiver.

Wallis, D. E.↗