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ADC - Analog to Digital Converter. Integrated circuit device used to digitize analog signal inputs so that they can be processed by a computer. The Spectral Engine uses a variety of ADCs to digitize analog video signals for imaging, and analog PHA signals for x-ray microanalysis.
SEI - Spectral Engine One. First-generation 4pi Spectral Engine computer card. This card works in NuBus Macintoshes only and consists of a Greenspring Computers 68020 host card plus a 4pi Spectral Engine daughtercard. It is typically connected via two 50-pin ribbon cables to a low profile SIU.
SEII - Spectral Engine Two. Second-generation 4pi Spectral Engine computer card, manufactured in several versions:
SIU - Scanning Interface Unit. External control box that connects the Spectral Engine computer card to the electron microscope and/or pulse processor. Depending on the application, the SIU provides buffering and independent control of scan signals, analog video signals, and PHA signals, thus allowing the Spectral Engine to be interfaced to a wide variety of electron microscopes and pulse processors.
PHA - Pulse Height Analysis or Pulse Height Analyzer. The process or device for precisely measuring the height of the analog voltage pulses from a pulse processor. The Spectral Engine ADC digitizes the pulse heights into 4096 bins, each bin representing a particular energy range.
ROI - Region of Interest. A defined X-ray energy range, usually associated with the approximate width of the X-ray spectrum for a particular element.
SCA - Single Channel Analyzer. A hardware or software device that discriminates over a wide range of X-ray energy signals and generates a discrete yes-no output for a selected ROI.
EDX - Energy Dispersive Spectroscopy. Technique to generate an X-Ray spectrum from electron bombardment. A detector collects X-rays and produces current pulses proportional to X-Ray energy; a pulse processor acts as a matched filter to convert the signal to analog voltage pulses. The PHA section of the Spectral Engine measures and records the pulse heights, and thus the energies of the X-Rays. The information is used to create an X-ray spectrum, a plot of counts detected versus X-ray energy. The spectrum can be acquired in probe mode (stationary beam) or in scanning mode (moving beam).
WDS - Wavelength Dispersive Spectroscopy. Technique to generate an X-Ray spectrum from electron bombardment. The technique differs from EDX in that a crystal spectrometer is inserted between the sample and the detector, creating large dispersion and high selectivity in detecting X-Ray energies; a hardware SCA typically generates a logic pulse for each x-ray detected in the wavelength selector range. The TTL count-rate section of the Spectral Engine measures and records these logic pulses. The information is used to create an X-ray map, an image of X-ray counts detected in a particular energy range at each pixel.
SEM - Scanning Electron Microscope. Refers either to the instrument, or the imaging part of the 4pi Spectral Engine hardware. The instrument uses a beam of electrons which is scanned in a raster over the sample. Various detectors, the most common being a Secondary Electron detector, produce a voltage corresponding to the response of the sample to the beam at each point in the scan. The 4pi system controls the scan and reads the detector to produce an image.
S(T)EM - Scanning (Transmission) Electron Microscope. An option for a Transmisson Electron Microscope to allow it to operate like a SEM.
EBIC - Electron Beam Induced Current.
TTL - Transistor-Transistor Logic. More commonly, the name of a class of integrated circuits operating at discrete levels of 0 and +5 volts. Typically, 0 to +0.8 volts is defined as logic level 0, +2.3 to +5 volts as logic level 1 (these definitions may be reversed).
CMOS - Complementary Metal Oxide Semiconductor. More commonly, the name of a class of low-power integrated circuits operating at discrete levels of 0 and +V volts. Unlike TTL, CMOS circuitry is capable of operating at levels higher than +5 volts, thus enhancing noise immunity. Typically, 0 volts is defined as logic level 0, +V volts as logic level 1 (these definitions may be reversed). In PC-compatible computers, CMOS refers to the battery-backed non volitile memory which stores BIOS and system configuration settings.
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