Pcm telemtry- a new approach using all- magnetic techniques

Digital all-magnetic circuit technique used in pulse code modulation telemetry system

Index to NASA Tech Briefs, January - June 1967

Technological innovations for January-June 1967, abstracts and subject inde

Electronics for Sensors

The aim of this Special Issue is to explore new advanced solutions in electronic systems and interfaces to be employed in sensors, describing best practices, implementations, and applications. The selected papers in particular concern photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs) interfaces and applications, techniques for monitoring radiation levels, electronics for biomedical applications, design and applications of time-to-digital converters, interfaces for image sensors, and general-purpose theory and topologies for electronic interfaces

Practical quantum realization of the ampere from the electron charge

One major change of the future revision of the International System of Units (SI) is a new definition of the ampere based on the elementary charge \emph{e}. Replacing the former definition based on Amp\`ere's force law will allow one to fully benefit from quantum physics to realize the ampere. However, a quantum realization of the ampere from \emph{e}, accurate to within $10^{-8}$ in relative value and fulfilling traceability needs, is still missing despite many efforts have been spent for the development of single-electron tunneling devices. Starting again with Ohm's law, applied here in a quantum circuit combining the quantum Hall resistance and Josephson voltage standards with a superconducting cryogenic amplifier, we report on a practical and universal programmable quantum current generator. We demonstrate that currents generated in the milliampere range are quantized in terms of $ef_\mathrm{J}$ ($f_\mathrm{J}$ is the Josephson frequency) with a measurement uncertainty of $10^{-8}$. This new quantum current source, able to deliver such accurate currents down to the microampere range, can greatly improve the current measurement traceability, as demonstrated with the calibrations of digital ammeters. Beyond, it opens the way to further developments in metrology and in fundamental physics, such as a quantum multimeter or new accurate comparisons to single electron pumps.Comment: 15 pages, 4 figure

An Adaptive Partial Response Data Channel for Hard Disk Magnetic Recording

An adaptive data channel is proposed which is better able to deal with the variations in performance typically found in the recording components of a hard disk drive. Three such categories of variation were investigated in order to gain an understanding of their relative and absolute significance; variations over radius, along the track length, and between different head / media pairs. The variations were characterised in terms of their effects on the step-response pulse width and signal-to-noise ratio. It was found that in each of the categories investigated, significant variations could be found in both longitudinal and perpendicular recording systems which, with the exception of radial variations, were nondeterministic over different head / media pairs but were deterministic for any particular head / media pair characterised. Conventional data channel design assumes such variations are non-deterministic and is therefore designed to provide the minimum error rate performance for the worst case expected recording performance within the range of accepted manufacturing tolerance. The proposed adaptive channel works on the principle that once a particular set of recording components are assembled into the disk drive, such variations become deterministic if they are able to be characterised. Such ability is facilitated by the recent introduction of partial response signalling to hard disk magnetic recording which brings with it the discrete-time sampler and the ability of the microprocessor to analyse signals digitally much more easily than analogue domain alternatives. Simple methods of measuring the step-response pulse width and signal to noise ratio with the partial response channel's electronic components are presented. The expected error rate as a function of recording density and signal to noise ratio is derived experimentally for the PR4 and EPR4 classes of partial response. On the basis of this information and the recording performance it has measured, the adaptive channel is able to implement either PR4 or EPR4 signalling and at any data rate. The capacity advantage over the non-adaptive approach is investigated for the variables previously identified. It is concluded on the basis of this investigation that the proposed adaptive channel could provide significant manufacturing yield and capacity advantages over the non-adaptive approach for a modest increase in electronic complexity

Vibrating transducers for fluid measurements

When a body vibrates in a fluid, some of the fluid is carried with it and the mass loading lowers its resonant frequency. Similarly, when compression of the fluid occurs, there is an added stiffness which by design can be made to predominate. In addition, there is an energy dissipation arising from viscous losses and acoustic radiation. The starting point of this research was a tuning fork with flat rectangular tines, designed to trap a narrow laminar of gas which is forced to pump in and out as the tines vibrate. The increase in kinetic energy, contributed by this high velocity' gas, gives the device a relatively large sensi ti vi ty as a gas density transducer. The change in frequency between vacuum and atmospheric pressure is typically a few percent, during which period the mechanical "Q" remains high enough to keep the fork sharply resonant. A high stability oscillator incorporating the transducer as the frequency controlling element was built. Small piezoelectric Cp2t) elements were used to drive the transducer and pick up the vibrations. A typical stability, equivalent to a pressure change of 0. 05 mBar was achieved. The supporting equipment re qui red for the work centred around a vacuum system with facilities for introducing a range of gases at precise rates. Computer control enabled the transducer's temperature, frequency, and "Q" factor to be measured and stored as the gas pressure was increased from vacuum. Extensive experiments were carried out on a range of tuning fork transducers, including a circular one in which a pair of disks clamped at the center acted as the tines and gave a simple radial gas displacement. Common to all these transducers is, the linearity of 1/f 2 with gas density for pressures above about 50 mBar; a departure from. linearity below this pressure; and below 10 mBar an overriding stiffness effect, where from vacuum to a few mBar the frequency paradoxically increases. The resultant calibration to this non-linear response, while exhibiting high stablility, is unattractive for general use. It has however applications over limited ranges as for example, those of a barometer or altimeter. Insight gained from experience with the double disk resonator, led to a new geometry which has resulted in an extremely viable transducer, without calibration anomalies, and capable of operating in a pressure or dehsity mode. Here, the gas is confined in two cylindrical cavities above and below a thin circular diaphragm, clamped at the periphery and again made to vibrate using p2t elements. In the fundamental mode, the alternating change in cavity volume due to compression and rarefaction of the gas, adds stiffness to the diaphragm. In the next mode, there is no net volume change, but the gas is pumped across the cavities adding inertial loading. No anomalies were experienced in the empirical calibrations obtained for each mode- the fundamental being linear with pressure Cf 2 proportional to Pl, and the first overtone linear with density (1/f 2 proportional to pl. A simple theory, which is sufficiently accurate for general design purposes, has been developed. Future work, which is of a straightforward development nature, is proposed. The high degree of stability achieved for these vibrating structures was later realised in a different geometry. In this, a long rod was excited into a torsional mode so as to produce two nodes a quarter wavelength from. either end. By securing the rod at these points and immersing the lower length in a liquid, a sensitive, robust, viscometer was produced. Driving the rod with a burst of oscillations, shears the liquid in contact with it. By removing this drive and measuring the rate of vibrational decay under the action of viscous dissipatiop, an indication of the viscosity can be obtained. The features of a pure shearing force, and the real-time, on-line nature of the device, makes it attractive for the characterisation of both thick and thin liquids and automatic process control

Fluidic hydrogen detector production prototype development

A hydrogen gas sensor that can replace catalytic combustion sensors used to detect leaks in the liquid hydrogen transfer systems at Kennedy Space Center was developed. A fluidic sensor concept, based on the principle that the frequency of a fluidic oscillator is proportional to the square root of the molecular weight of its operating fluid, was utilized. To minimize sensitivity to pressure and temperature fluctuations, and to make the sensor specific for hydrogen, two oscillators are used. One oscillator operates on sample gas containing hydrogen, while the other operates on sample gas with the hydrogen converted to steam. The conversion is accomplished with a small catalytic converter. The frequency difference is taken, and the hydrogen concentration computed with a simple digital processing circuit. The output from the sensor is an analog signal proportional to hydrogen content. The sensor is shown to be accurate and insensitive to severe environmental disturbances. It is also specific for hydrogen, even with large helium concentrations in the sample gas