Data Acquisition Cycle Research Articles

4698593 Apparatus and method for T1 NMR imaging using spin echo NMR responses elicited by initial excitation pulses of differing nutation values

NMR response data usable to form a T1 NMR image is obtained by using constant repetition rate data acquisition cycles but wherein different initial nuclei nutation angles are employed to elicit NMR spin echo signal responses. Because of the different initial nutation angles employed to elicit the NMR responses, those responses will differ in accordance with an exponential function of the T1 spin-lattice relaxation time constant of the region under test. Once such T1-dependent data is captured, the T1 time constant may be calculated or otherwise derived (e.g. by an empirical best fit to an exponential curve of known time constant) to produce a T1 value for each incremental volume element (voxel) of the volume under test (e.g. a planar volume). In this manner a visual image of the T1 NMR parameter is created when the complete array of derived T1 values is converted to gray-scale (or color) values and displayed as corresponding picture elements (pixels) in a raster-scanned CRT display or the like. Such an approach may provide a significant speed improvement in the overall data acquisition time required to derive a T1 NMR image. Such speed improvements may be especially useful where large numbers of multiple slices through the object under test are being examined.

Data Acquisition and Process Control Software Automates Entire Cycles

Data Acquisition and Process Control Software Automates Entire Cycles

Computer-controlled system for investigating the hydrostatic piezoresistive effect as a function of temperature

A system has been developed for investigating the piezoresistive effect in semiconducting solids and conductive polymers under different elastic and thermal boundary conditions. The system provides the necessary information needed for sensor design such as nonlinearity, hysteresis, and temperature dependence of the piezoresistance coefficient. The system operates under full computer control for both data acquisition and data reduction cycles. The temperature dependence of the hydrostatic piezoresistance coefficient of a donor-doped polycrystalline semiconducting barium titanate below and above its ferroelectric–paraelectric Curie point will be presented for the first time. The nonlinear and hysteretic behavior of an electrically conductive polymer over the pressure range of 0–30 MPa will also be demonstrated.

Computer controlled facility for measurement of the bidirectional scattering distribution function

A computer controlled facility for measurement of the bidirectional scattering distribution function is described, with application to the evaluation of spacecraft surface contamination in optical and thermal control systems. An automatic detector/sampleholder allows a 360-deg detector scan around the sample for a complete bidirectional reflectance and transmittance distribution function characterization. The system demonstrates reduced data acquisition and reduction cycle time, and improved accuracy.

CAMAC Data Scanner with LRS4299 DATABUS Interface

A CAMAC data scanner was designed and manufactured. The scanner is in conformance with LeCroy's 4290 series DATABUS interface. The scanner supports CAMAC single action and block transfer mode with zero suppress capability. The S2 timing of CAMAC cycle may be skipped to squeeze data acquisition cycle. The scanners are located at front-end CAMAC crates in the FASTBUS based TOPAZ data acquisition system.

High Precision Scanning Ellipsometer

We describe the design, construction, alignment, and calibration of a photometric ellipsometer of the rotating-analyzer type. Data are obtained by digital sampling of the transmitted flux with an analog-to-digital converter, followed by Fourier transforming of the accumulated data with a dedicated minicomputer. With an operating mechanical rotation frequency of 74 Hz, a data acquisition cycle requires less than 7 msec. The intrinsic precision attainable is high because precision is limited only by shot noise or intrinsic source instabilities, even when relatively weak continuum lamps are used as light sources. Precision may be improved by accumulating the data for consecutive cycles at a fixed wavelength. The system allows complex reflectance ratios to be determined as continuous functions of wavelength from the near infrared to the near ultraviolet spectral range. Data reduction programs can be modified to calculate complex refractive index or dielectric function spectra, or film thicknesses and refractive indices, as well as the usual ellipsometric parameters tanpsi, cosDelta.

Interim Data Acquisition System for the Environmental Test Laboratory

An interim data acquisition (IDAC) system was developed and installed in the Environmental Test Laboratory of the Applied Physics Laboratory. This system can scan 200 analog voltages and 400 thermocouples under control of a programmable calculator. The calculator converts the data to engineering units, checks calibration channels for out-of-tolerance and thermocouples for open circuit. Source and channel identification is formatted with the data and printed at the rate of approximately 1 channel/s. Also included in this printout are power-supply wattages calculated from measured voltages and currents, and temperature averages for preselected groups of thermocouples. Out-of-tolerance calibration channels and open thermocouples are flagged when they are printed out. A digital clock provides timed intervals for automatically initiating the data acquisition cycle. Time and test identification data are pointed at the start of each printout to identify test and run numbers.