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Functional Description
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The Scan Acquisition Processor/Waveform Generator Board
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The scan acquisition processor/waveform generator (SAP/Wave) board
is a real-time control and acquisition microcomputer that makes use of
an 80C186 microprocessor. The SAP/Wave board communicates with
the data system via an IEEE-488 interface board installed in the data
system computer bus. The SAP/ Waveboard performs the following
functions:
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Interprets instrument commands from the data system and produces a
sequence of analog and digital signals that control operation of circuits
on other Saturn GC/MS boards.
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Collects analog and digital diagnostic data from other subsystems and
transmits that information to the data system.
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Filters, integrates and digitizes the ion current signal and transmits the
spectra to the data system.
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Generates axial modulation waveforms, including waveforms used by
SECI, MS/MS and SIS options.
Upon power-up, the 80C186 processor runs a ROM resident program that
initializes the board. The program permits the processor to receive information
through the IEEE-488 interface. When you start up the Saturn data system,
operating information is downloaded to the SAP/Wave board’s RAM memory.
The SAP/Wave board then performs its operations in response to the commands
sent through the IEEE-488 interface.
NOTE: The SAP/Wave board is accessed through two connectors on the rear
panel of the instrument. J42 is an IEEE connection used for interconnection to
the Data System. J43 is a D-shell connector labeled ‘Remote Option’ and is
used for special research applications and the GC start signal.
When a mass spectrum is acquired, the data system downloads parameters
such as electron multiplier voltage, scan range and time, ionization mode, etc.
The SAP/Wave board uses this information to create a scan over the desired
mass range. During the scan, ion current data is accumulated and, at the end of
the desired scan time, sent to the data system for further processing and display.
The waveform generator is capable of generating waveforms over a wide range
of frequencies and amplitudes. The data system produces a digital version of the
desired time domain waveform, and downloads the resulting binary file RAM. At
the appropriate time, the data is clocked out of the RAM into a waveform
reconstruction DAC. The DAC output is then filtered to remove undesirable
frequencies. The Saturn GC/MS uses the waveform generator in chemical-
ionization (SECI), MS/MS, or SIS applications; as well as in normal axial
modulation.
Characteristics of the waveform generator include the following:
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Dual-port RAM (256 Kbytes) to provide memory for single or multiple
digitized waveforms
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A selectable frequency generation clock (625 KHz, 1.25 MHz, or 2.5
MHz and a 15-bit variable length counter to control timing
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A 12-bit DAC, low pass filter and amplifier to reconstruct waveforms
