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At least 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS1961

Methods for Determining Blood Flow Through Intact Vessels of Experimental Animals Under Conditions of Gravitational Stress and in Extraterrestrial Space Capsules

Work during the initial six months of this program has proceeded along three lines: (1) technical development of blood flowmeter instrumentation: (2) surgical considerations related to special problems of chronic implantation of flowmeter probes: (3) study of the relationship between levels of blood flow and organ activity. Principal engineering effort has been focused on the fundamental phenomena operative in the flowmeter probe and on probe design. Two probes have been constructed and a third is nearing completion. A previously unrecognized source of zero drift has been discovered and corrected. has been designed, assembled, tested and successfully employed in work on the several probes. A significant innovation which has been introduced is the use of a transformer coupled input for suppression of unwanted common mode signals. New low noise transistor amplifiers with characteristics suitable for space vehicle packaging are being developed. Linearity of the present apparatus has been found to extend at least into the near turbulent flow region. Attention has been directed to the two vascular beds of physiologic interest that present particular problems with regard to chronic implantation of flowmeter probes, the myocardium and the liver. Surgical techniques have been perfected that will permit myocardial and liver blood flow measurement. Two groups of animals have successfully undergone surgery and await the implantation of probes. Studies of the relationship between organ blood flow and levels of physiologic activity have been initiated. The first organ system studied was the heart, For the first time autoregulatory mechanisms have been demonstrated within the myocardial vascular bed which rapidly and precisely maintain coronary blood flow at a level i n keeping with the magnitude of cardiac work, Following a summary statement of the status of the program, the work performed is described, A financial review of expenditures incurred and a proposal for future funding are appended,

Shaw, R. F.↗

NASA NTRS1965

Tiny biomedical amplifier combines high performance, low power drain

Transistorized, portable, high performance amplifier with low power drain facilitates biomedical studies on mobile subjects. This device, which utilizes a differential input to obtain a common-mode rejection, is used for amplifying electrocardiogram and electromyogram signals.

Deboo, G. J.↗

NASA NTRS1968

Amplifier improvement circuit

Stable input stage was designed for the use with a integrated circuit operational amplifier to provide improved performance as an instrumentation-type amplifier. The circuit provides high input impedance, stable gain, good common mode rejection, very low drift, and low output impedance.

Sturman, J.↗

NASA NTRS1970

Redundant electronic circuit provides fail-safe control

Circuit using dual control amplifiers and dual position demand potentiometers powered from separate sources is used for reliable hydraulic valve controller that prevents closure of valve when control circuits fail, and maintains valve control to close tolerance for more common modes of controller failure.

Archer, J. W.↗

NASA NTRS1972

Stable photosensor amplifiers

Minimization of common mode effects in differential amplifier arrangement which processes signals from two high impedance photosensors is achieved by connecting one photosensor in feedback loop of amplifier and using field effect transistors in the input circuit.

Fujimoto, H.↗

NASA NTRS1972

Rebalance electronics

Two basic types of strapdown gyroscope rebalance-electronics were analyzed and compared. These two types were a discrete-pulse ternary system and a width-modulated binary system. In the analyses, major emphasis was placed on the logic sections, the H-switches, the precision voltage reference loops, the noise performance, common-mode rejection, and loop compensation. Results of the analyses were used in identifying specific advantages and disadvantages of system details and in making accuracy and resolution comparisons. Sound engineering principles were applied in the development of both systems; however, it was concluded that each system has some disadvantages that are amenable to improvement.

Blalock, T. V.↗

NASA NTRS1974

Low cost instrumentation amplifier

Amplifier can be used for many applications requiring high input impedance and common mode rejection, low drift, and gain accuracy on order of one percent. Performance of inexpensive amplifier approaches that of some commercial instrumentation amplifiers in many specifications.

Sturman, J. C.↗

NASA NTRS1974

ASTP simulated lightning test report

A simulated lightning test was conducted on the backup spacecraft for the Apollo Soyuz Test Project mission (CSM-119) to determine the susceptibility of the Apollo spacecraft to damage from the indirect effects of lightning. It is demonstrated that induced lightning effects from low-level injected currents can be scaled linearly to those which are obtained in a full threat lightning stroke. Test results indicate that: (1) many of the power and signal critical circuits would fail if subjected to full-threat lightning, (2) pyrotechnic circuits are safe for full-threat lightning, and (3) common-mode voltages exceeded the failure criteria level for all but three of the circuits tested.

Blount, R. L.↗

NASA NTRS1977

Inexpensive pulse-train converter measures analog voltage

Converter measures small voltages or currents in presence of very large common-mode voltages (thousands of volts ac or dc). Advantages are low power consumption, transmission via single isolated channel, simplicity, and operation from single-polarity power supply.

Sturman, J. C.↗

NASA NTRS1979

Hybrid ECG signal conditioner

Circuit with high common-mode rejection has ability to filter and amplify accepted analog electrocardiogram (ECG) signals of varying amplitude, shape, and polarity. In addition, low power circuit develops standardized pulses that can be counted and averaged by heart/breath rate processor.

Rinard, G. A.↗

NASA NTRS1982

Retrofit energy conservation in residential buildings in southern California

The common energy conservation techniques (ECTs) that can be retrofit-installed into residential buildings are surveyed. The quantity of saved energy for heating and cooling attributable to each ECT is evaluated for three common modes of heating: natural gas heating at 60/therm; heating via heat pump at $1.20/therm; and electric resistance heating at $2.40/therm. In every case, a life cycle cost comparison is made between the long term revenue due to energy conservation and a safe and conventional alternative investment that might be available to the prudent homeowner. The comparison between investment in an ECT and the alternative investment is brought into perspective using the life cycle payback period and an economic Figure of Merit (FOM). The FOM allows for relative ranking between candidate ECTs. Because the entire spectrum of winter heating climates in California is surveyed, the decision maker can determine whether or not a considered ECT is recommended in a given climate, and under what conditions an ECT investment becomes attractive.

Turner, R. H.↗

NASA NTRS1985

Circuit transients due to negative bias arcs on a high-voltage solar array in low Earth orbit

Arcing to negatively biased, exposed solar cell interconnects on solar arrays placed in plasma environments was established. Arcing, however, may cause damaging interference with the operation of electrical power systems in spacecraft planned to be driven with high-voltage solar arrays. An analytical model was developed to estimate the effects of netagive bias arcs on solar array power system performance. Solar cell characteristics, plasma interactions, and power system features are modeled by a linear, lumped element transient circuit, and the time domain equations are solved. Numerical results for solar array common mode and load voltage transients are calculated for typical conditions. Acceptable load transients are found for a range of arc current amplitudes and time constants.

Metz, R. N.↗

NASA NTRS1986

Software fault-tolerance by design diversity DEDIX: A tool for experiments

The use of multiple versions of a computer program, independently designed from a common specification, to reduce the effects of an error is discussed. If these versions are designed by independent programming teams, it is expected that a fault in one version will not have the same behavior as any fault in the other versions. Since the errors in the output of the versions are different and uncorrelated, it is possible to run the versions concurrently, cross-check their results at prespecified points, and mask errors. A DEsign DIversity eXperiments (DEDIX) testbed was implemented to study the influence of common mode errors which can result in a failure of the entire system. The layered design of DEDIX and its decision algorithm are described.

Avizienis, A.↗

NASA NTRS1986

Circuit transients due to negative bias arcs-II

Two new models of negative-bias arcing on a solar cell power system in Low Earth Orbit are presented. One is an extended, analytical model and the other is a non-linear, numerical model. The models are based on an earlier analytical model in which the interactions between solar cell interconnects and the space plasma as well as the parameters of the power circuit are approximated linearly. Transient voltages due to arcs struck at the negative thermal of the solar panel are calculated in the time domain. The new models treat, respectively, further linear effects within the solar panel load circuit and non-linear effects associated with the plasma interactions. Results of computer calculations with the models show common-mode voltage transients of the electrically floating solar panel struck by an arc comparable to the early model but load transients that differ substantially from the early model. In particular, load transients of the non-linear model can be more than twice as great as those of the early model and more than twenty times as great as the extended, linear model.

Metz, R. N.↗

NASA NTRS1986

Superconducting gravity gradiometer for space and terrestrial applications

A three-axis superconducting gravity gradiometer with a potential sensitivity better than Eotvos per sq root Hz is currently under development for applications in space. Although such a high sensitivity may be needed for only a limited number of terrestrial applications, superconductivity offers many extraordinary effects which can be used to obtain a gravity gradiometer with other characteristics necessary for operation in a hostile moving-base environment. Utilizing a number of recently devised techniques which rely on certain properties of superconductors, a design for a sensitive yet rugged gravity gradiometer with a high degree of stability and a common-mode rejection ratio greater than 10 to the 9th is produced. With a base line of 0.11 m, a sensitivity of 0.1 Eotvos per sq root Hz is expected in an environment monitored to a level of 0.01 m/sq sec sq root Hz for linear vibration and 7 x 10 to the -6th rad/s sq root Hz for angular vibration. A conventional stabilized platform can be used at this level. The intrinsic noise level, which is two orders of magnitude lower, could be achieved by monitoring the attitude with a superconducting angular accelerometer which is under development. In addition, the new gradiometer design has the versatility of adapting the instrument to different gravity biases by adjusting stored dc currents.

Moody, M. V.↗

NASA NTRS1986

Software reliability - Measures and effects in flight critical digital avionics systems

The paper discusses software reliability as it applies particularly to design and evaluation of flight-critical digital avionics systems. Measures of software reliability, measurement methods and reliability (macro-) models are discussed. Recent work assessing their accuracy in predicting software errors in 'fly-by-wire' Newtonian applications is presented. Additional, detailed topics are discussed including software error distributions (e.g. catastrophic vs. noncatastrophic) and the effects of system growth/maturity on reliability improvement. In practical flight-critical digital applications, software reliability improvement is sought through use of parallel, redundant software (i.e. N-version programming) or backup software that can be invoked in the event of (primary) software failure. Achievable reliability levels are however highly sensitive to common-mode specification and programming errors. Recent data correlating these errors with net software reliability are discussed.

Dunn, William R.↗

NASA NTRS1988

Electrically-Isolating Analog Amplifier

Signals transmitted between units at different ground potentials. Analog amplifier electrically isolates input from output through use of optoelectronic components. Analog isolation amplifier uses dual-transistor optoisolator, preventing transmission of common-mode voltage from input to output. Circuit useful in spacecraft electronic systems.

Paulkovich, John↗

NASA NTRS1987

Monocrystalline silicon gradiometer for gravity experiments in space

A very important research effort has been made in the last decade in the field of high precision measurement with laser instrumentation. The development of a space borne gradiometer operating at a high sensitivity level using laser measurement of the distance between proof mass over a short base line of order one meter is discussed. Two aspects of laser technology make it a promising tool for gradiometry measurements: quantum limited accuracy and absolute distance measurements. The quantum limit associated with laser instrumentation was formulated. The relevant quantum and classical sources of errors in laser measurements were reviewed and corresponding laser performance requirements for gradient measurements were evaluated. Some mechanical quality factor measurements were made on simple resonant monocrystalline silicon suspensions. It was discovered that the use of zero derivative restoring forces to position the gradiometer test masses will dramatically reduce the gradiometer temperature control requirements. A laser beam side injection scheme was discovered which permits rejection of common mode accelerations. These concepts are briefly discussed.

Richard, Jean-Paul↗