Showing papers on "Detector published in 1981"

Determination and correction of quadrature fringe measurement errors in interferometers

Abstract: The precision and accuracy of interferometers using quadrature fringe detection are often limited not by the interferometer itself but by the detector system. There are three typical errors: unequal gain in the two channels; quadrature phase shift error; and zero offsets. This paper describes a simple method for determining the quadrature errors from experimental data obtained in the interferometer and correcting for them. A numerical example demonstrating the significant improvement in the precision of interferometer data is given.

An improved endpoint detector for isolated word recognition

Abstract: Accurate location of the endpoints of an isolated word is important for reliable and robust word recognition. The endpoint detection problem is nontrivial for nonstationary backgrounds where artifacts (i.e., nonspeech events) may be introduced by the speaker, the recording environment, and the transmission system. Several techniques for the detection of the endpoints of isolated words recorded over a dialed-up telephone line were studied. The techniques were broadly classified as either explicit, implicit, or hybrid in concept. The explicit techniques for endpoint detection locate the endpoints prior to and independent of the recognition and decision stages of the system. For the implicit methods, the endpoints are determined solely by the recognition and decision stages of the system, i.e., there is no separate stage for endpoint detection. The hybrid techniques incorporate aspects from both the explicit and implicit methods. Investigations showed that the hybrid techniques consistently provided the best estimates for both of the word endpoints and, correspondingly, the highest recognition accuracy of the three classes studied. A hybrid end-point detector is proposed which gives a rejection rate of less than 0.5 percent, while providing recognition accuracy close to that obtained from hand-edited endpoints.

Charged particle behavior in low‐frequency geomagnetic pulsations 1. Transverse waves

Abstract: The behavior of charged particles in low-frequency geomagnetic pulsations is examined with particular emphasis on what a spacecraft-borne detector would observe. We concentrate on the effects of purely transverse electromagnetic signals. The time scale of a particle's motion relative to the wave period is shown to determine the nature of its response. For low-energy particles, the acceleration in the last gyroperiod before detection is what matters. At higher energies, what has occurred over recent bounce and drift motions becomes increasingly important and convection of gradients by the wave E × B drift must be considered. Distinguishing features such as phase differences between signals in back-to-back detectors or between channels of different energy are catalogued. In particular, we assess the detectability of resonance effects in the light of detector characteristics and finite signal bandwidth. Recent observations are used to illustrate the ideas developed.

Temporal summation of moving images by the human visual system.

Abstract: Measurements of threshold visibility were made as a function of duration of stimulus exposure for small moving dot targets, drifting sinusoidal gratings and moving patches of sinusoidal gratings, to investigate how the human visual nervous system summates over time signals arising from stimuli in motion. At image speeds of less that 16 deg/s, temporal summation is as strong and as extended for moving as for stationary dots (total summation over to about 100 ms). This summation is about twice that which would be expected from separate consideration of the regions of spatial and temporal integration. Measurements with sinusoidal gratings reveal that the nature of the summation depends critically on the spatial frequency of the stimulus: gratings of low spatial frequency summate well when in motion (and only when in motion), whereas those of high spatial frequency summate well only when stationary or in very slow motion. An analogue simulation with electronic filters showed that these psychophysical results are directly predictable from the known transfer characteristics of the human visual system (with the additional assumption of probability summation at threshold). Finally, with small patches of sinusoidal grating, it was established that translation per se across the retina has little effect on temporal summation. This suggests that the results obtained with sinusoidal gratings of large extent are also relevant to small moving stimuli, allowing the summation results obtained with dot stimuli to be discussed in terms of the temporal transfer properties of spatially selective visual detectors. On the basis of these results it is proposed that the extended temporal summation observed for dots in motion results from summation of energy of low spatial frequency present in these stimuli.

Ripple detector for automotive alternator battery charging systems

Abstract: Detector (28) monitoring the voltage ripple in the rectified electrical output signal of an alternator (22) in a multiphase alternator battery charging system. A circuit monitors the undulating alternator output signal and produces a signal level in response. To correct the detector operation for various magnetic phenomena present in the alternator, a first circuit measures the rotational speed of the rotor and produces a proportional signal. A second circuit determines the excitation current supplied to the field coil. The measurement and determination are separately weighted and combined to form a corrected comparison threshold value. A variable threshold circuit combines the signal proportional to the rotational speed of the rotor and the determined field coil excitation current to produce a combined signal level. Comparison means compare the signal level from the monitored alternator output signal with the combined signal level and produce an output signal level indicative of the detection of a voltage ripple in excess of the combined signal level. The output signal is corrected for the effects of significant alternator performance characteristics.

Scanning contaminant and defect detector

Abstract: A scanning laser contaminant and defect detector for reflective surfaces, having a light collector for increasing sensitivity to scattered light. The collector is preferably one quadrant of a spherical shell cradled between V-shaped reflective side walls. The collector has beam entrance and exit ports, as well as a detector port where a light detector resides. The collector is placed in proximity to a surface to be inspected. Light scattered from the test surface is directed to the reflective crown surface, then to the reflective side walls and ultimately to the detector.

Method and apparatus for light-induced scanning-microscope display of specimen parameters and of their distribution

Abstract: The invention contemplates scanning-microscope display of plural observed parameters of an examined specimen, where the parameters derive from flying-spot light-exposure of the specimen, and where at least one of the observed parameters is outside the wavelength range of the flying-spot. In some illustrative embodiments, at least one of the observed parameters is sensed by a detector which uses the same scanning optics as the flying-spot, and in other embodiments other techniques of synchronization are involved. The disclosed embodiments also provide for selective arrest of scanning to enable such factors as fading fluorescence and spectrum analysis to be ascertained strictly for a surface occlusion, impurity or other anomaly of interest.

Two dimensional image panel with range measurement capability

Abstract: A two dimensional optical array of lenslets and detectors is provided. The outputs of the detectors are combined to produce a signal indicative of the characteristics of an object being viewed while the output of selected detectors are compared to produce a signal indicative of the range to the object.

Weld quality monitor

Abstract: Weld arc voltage, weld arc current and weld arc travel speed are monitoredn a real-time basis during the welding process. Each monitored quantity or parameter is compared directly with a reference value indicative of a high quality weld, and an alarm is activated when a preselected variation in the measured and the reference quantities occurs. The monitored quantities are also used to calculate additional welding parameters, including heat input, weld bead area and cooling rate. These parameters are also compared to ideal reference values in order to control weld quality. The sensors used for measuring the welding parameters are selected so as to provide minimal interference with the welding process. For example, Hall effect transductors are used for current measurements, while a unique opto-electronic noncontacting sensor is used for measuring the weld speed.

Cello-A New Detector at PETRA

Abstract: A description of the design characteristics of CELLO, a large 4Π magnetic detector at PETRA, is given and first results of beam operation are presented.

Monte Carlo calculations of X-ray scatter data for diagnostic radiology

Abstract: X-ray scatter data have been calculated by Monte Carlo methods for diagnostic radiology applications. The scatter intensities relative to the primary intensities are given for different detectors for various values of object thickness, field size, object-to-detector distance, and primary energy. The results are compared the those from previous investigations. The calculations made it possible to resolve contradictions in published measurements regarding the dependence of scatter intensities on primary X-ray energy and detector response.

Detection of weak signals in non-Gaussian noise

Abstract: A locally optimum detector structure is derived for the detection of weak signals in non-Gaussian environments. Optimum performance is obtained by employing a zero-memory nonlinearity prior to the matched filter that would be optimum for detecting the signal were the noise Gaussian. The asymptotic detection performance of the locally optimum detector under non-Gaussian conditions is derived and compared with that for the corresponding detector optimized for operations in Gaussian noise. Numerical results for the asymptotic detection performance are shown for signal detection in noise environments of practical interest.

Monitoring system and method utilizing signal injection for determining channel reception of video receivers

Abstract: A system and method is provided for determining the channel to which a video wave receiver is tuned The system includes an RF signal source connected to the antenna input of the video wave receiver, a frequency control stage that determines the signal frequencies generated by the RF signal source and a system and advance control stage to appropriately program operation of the frequency control stage The RF signal source is conditioned by the system and advance control stage and the frequency control stage to output signals such that the fundamental or one of the harmonics when combined with the video carrier of a corresponding channel results in a signal having a predetermined frequency The RF signal source is successively advanced to output a set of predetermined frequencies, corresponding to each of the receivable channels to which the video receiver is tunable The system includes a detector/receiver arranged to monitor the video signal of the video receiver to detect the predetermined frequency resulting from the combined signal from the RF signal source and a video carrier to which the video receiver is tuned The RF signal source is stepped through a predetermined set of frequencies corresponding to each receivable channel and the system outputs a signal denoting the received channel to which the video receiver is tuned when the predetermined frequency is detected by the detector/receiver

Anti-theft control system

Abstract: The anti-theft control system includes a sending module (A) for sending encoded signals on a power line (12) of a vehicle power supply (B). The sending module (A) includes a keyboard (52) on which an authorized user enters his code. If the proper code is entered, a digital encoder (40) produces a preselected encoded signal which is imposed on the power signal by an interface circuit (60). The anti-theft control system further includes a receiving module (C) which receives encoded signals from the power line. The receiving module includes a detector (70) for separating encoded signals from the power signal and a decoder (80) for comparing the received encoded signal with the preselected encoded signal. If the decoder (80) determines that the preselected encoded signal has been received, it enables an ignition control circuit (90) to pass electric power from the vehicle ignition key switch (20) to the vehicle ignition (22). Optionally, an alarm control circuit (100) may enable an alarm a predetermined time determined by delay timer (114), after the vehicle is entered unless the alarm control circuit (100) is disabled by the detector (80).

System for detecting bubble formation in clear and opaque fluids

Abstract: A system for use in flow metering apparatus for detecting bubble formation in both clear and opaque fluids in an administration set includes a light source and a light detector positioned on opposite sides of a transparent tubing segment of the administration set such that light transmitted through the tubing to the detector is dependent on the presence or absence of fluid in the tubing. With clear fluid present, a first comparator in the system interrupts operation of the metering apparatus when the light detector output falls below a predetermined minimum level. With opaque fluid present, a second comparator interrupts operation of the apparatus when the light detector output rises above a predetermined maximum level. The detection system is automatically conditioned to either clear or opaque operating modes without input from the operator, and incorporates protection circuitry for interrupting operation of the metering apparatus in the event of failure of either the light source or the light detector.

A tone oriented voice excited vocoder

Abstract: An LPC base-band vocoder is developed. The novel feature concerns the coding of the base-band. A model is set up for the base-band as a set of modulated tones. Algorithms are presented for the extraction of amplitude and phase/frequency of the tones. Implementation aspects as well as simulation results are discussed. Total bit rates in the order of 3,2-4.8 kbits are possible where approximately one half of the bits represents the base-band coding. Experiments have shown the coder to be robust to background noise.

Detection of spatially nonuniform ultrasonic radiation with phase sensitive (piezoelectric) and phase insensitive (acoustoelectric) receivers

Abstract: An analysis is presented of the responses of a phase sensitive and a phase insensitive ultrasound receiver detecting a spatially nonuniform pressure distribution. The predicted output of each type of receiver is obtained numerically using a model of wave propagation based upon diffraction theory. Experimental verification of these predictions is obtained using a piezoelectric and an acoustoelectric receiver as a phase sensitive and a phase insensitive detector, respectively. Results are illustrated for transmission measurements of the frequency‐dependent attenuation of an irregular plastic plate and for scattering measurements of the observed angular and spatial dependence of scattering from a pair of brass rods.

Compact subharmonic mixer for EHF wave receiver using a single wave guide and receiver utilizing such a mixer

Abstract: A subharmonic mixer, whose local oscillator is at half the frequency of that of the signal to be received, comprising a detector and a local oscillator positioned in a single waveguide (301). The mixer comprises a first module (51) serving as the local oscillator and incorporating an oscillation diode surrounded by dielectric material and connected to a wide metal coating, as well as a second module (52) incorporating an antiparallel connection of two Schottky diodes and which is identical to the first module. The metal coatings of these two modules are in contact with metallized areas (53, 54) of a double-faced printed circuit (15) serving for the polarization of one module and for the signal output of the other.

A Surface Acoustic Wave Gas Detector

Abstract: : Experimental results are presented on a new type of gas detector employing surface acoustic waves (SAW's). The SAW piezoelectric gas detector (SAWPG) consists of twin SAW delay lines fabricated on a single piezoelectric substrate each connected in an oscillator configuration. The propagation path of one delay line oscillator is coated with a selectively sorbent film, while the other is uncoated and used as a stable reference. Changes in phase delay resulting from mass loading or stress effects induced by gases sorbed on the delay line containing the film result in corresponding frequency shifts relative to the reference oscillator that are proportional to gas concentration. Since SAW energy is concentrated near the film, the detector is found to be highly sensitive. Further, the SAWPC offers the means to detect any gas given the corresponding selectively sorbent film.

Method for simultaneous teletext and analog signal transmission

Abstract: Disclosed is a process for the transmission of information over television networks wherein certain information is encoded in digital form and transmitted by supplementing and/or replacing the information forming the conventional program. The digital information is received by a conventional receiving set equipped with a decoding, memory and detector means. Information is transmitted in the form of analog signals subdivided into scans or groups of scans, each scan having associated identifying material. The information transmitted in digital form has other identifying material and is transmitted generally synchronously with the corresponding information in analog form. The transmissions are received by receivers with detectors sensitive to the identifying material and which have analog-digital and inverse conversion means as well as memory and decoding means to reproduce the information contained in the analog and digital signals.

Planar multimode detector arrays for infrared and millimeter-wave applications

Abstract: A new type of detector array is described. By means of a suitably designed metallic network, many detector elements (each individually small compared to wavelength) are assembled into an impedance-matched termination for radiation incident normally on the plane of the device. Residual reactance is tuned out by means of a movable backshort. An array of 400 bismuth-film microbolometers with a total area of 1 cm2has been tested at 215 GHz. A coupling efficiency of approximately 60 percent was observed. The detector has a D* of 4 \times 10^{8} cm . Hz1/2/W at room temperature with response time on the order of 2 \times 10^{-7} s. Similar arrays of Schottky and SIS diodes can probably be constructed.

A high-efficiency two-dimensional angular correlation spectrometer for positron studies

Abstract: A two-dimensional angular correlation spectrometer based on position sensitive Anger camera detectors is described. The specification of the machine includes an angular resolution of 0.65 mrad FWHM by 0.65 mrad FWHM over an angular field of order 21*21 mrad2 and an exceptionally high efficiency for counting coincidence events. The spectrometer design is discussed in the light of the basic measurement problem and its performance is illustrated with the aid of the results of explicit test measurements and some representative results.

Portable combination lamp, smoke detector and power failure alarm

Abstract: A portable protection device is shown for use in sounding a warning in the event of smoke or power failure and to supply a portable high intensity lamp when needed. The unit is enclosed in a small, light weight portable housing and includes a smoke alarm, a high intensity lamp and a power failure alarm all operable from an AC line source or from a self contained DC battery source. The device is useful for travelers at hotels, students at dormitories, and the like.

Multilevel liquid sensing system

Abstract: A conductive multilevel liquid sensor uses conventional integrated circuits such as inverters and voltage comparators as signal detectors, and a flat cable having corrosion-resistant probe conductors of different lengths as the sensing probe assembly. The binary encoded outputs of the signal detectors identify the sensed liquid level. A continuous level control is realized by the addition of timing logic, and sensor operation range is improved by having the voltage at one comparator input be adaptive to the change in liquid conductivity.

Design Considerations for Positron Emission Tomography

Abstract: The surge of interest in medical research with positron-emitting nuclides has been accompanied by improvements in the design of positron emission tomographs (scanners). Bismuth germanate has emerged as the scintillation material of choice for high resolution scanners, as its detection efficiency with small crystals is higher than that of NaI. Other detector materials, such as CsF, may be useful when timing accuracy is of great importance, as in high count rate studies or time-of-flight measurements. Circular detector arrays are now generally preferred because they provide the best sensitivity and uniformity of coverage. Multiple rings are used to increase the axial coverage. Other design parameters, such as detector and collimator dimensions, are surveyed and their effect on scanner performance is discussed.

Radiation heat loss detector.

Abstract: Need for a simple to use device that gives good estimates of heat loss from a building or machines exists This device uses a radiation and convection heat loss detector to answer this need Radiation from an extended surface area as at (22) is detected with a sensor (40) having a wide field of view closely matching that of an associated camera (24) By simultaneously photographing the surface area at (22) of interest and detecting the radiation from that same area at (22), a clear record as in Fig 2 is provided for future use A wide band radiation sensor (40) is used Compensation for environmental radiation is made by first viewing the environment with the sensor (40) and holding the sensed signal and then subtracting that signal from the flux detected when the sensor (40) faces the extended surface area The date and time are also recorded on the photograph as in Fig 2 A sonar device (42) positioned on the camera provides a distance indication which, with a known field of view, allows for a determination of the total flux from the surface area at (22), a determination of convective heat losses from the surface and correction for atmospheric absorption of the radiant energy