A Microcomputer System for Real-Time Monitoring and Control of Gas Chromatographs
TL;DR: A microcomputer system based on the Intel 8008 microprocessor has been developed to perform real-time, on-line data acquisition and analysis of gas Chromatographic data, and to control sampling and operation of the gas chromatograph.
Abstract: LBL-4138 A microcomputer system based on the Intel 8008 microprocessor has been .developed to perform real-time, on-line data acquisition and analysis of gas chromatographic data, and to control sampling and operation of the gas chromatograph. Real-time analysis is achieved by the novel method of interleaving subprograms for the sequential data acquisition and reduction steps, thereby minimizing memory requirements. The system contaiils a real-time clock for signal timing,and interfaces to a teletype and digital volt meter. A digital-to-analog converter is used to control the temperature of the gas chromatographic column, while a matrix of relays is able to actuate sampling values.
Summary (1 min read)
The Microcomputer System
- A microcomputer system based on the Intel 8008 microprocessor was constructed using the bin-oriented modular approach developed at the .
- Logic cards supporting integrated circuits are connected together by a forty-wire bus whichcontrols input, output, memory storage and timing functions.
- An important feature of the microcomputer controller is the direct digital control (DDC) of the column heater.
- A method offering greater precision and low cost is the combination of a digitally controlled timer with a solid-state >triac .
- The counter starts a count-up sequence until the carry bit is set, whereupon the counter overflows in a time less than 1/120 sec (half-cycle period).
- The microcomputer system was experimentally tested in separate process-control and analytical studies.
- The program behavior was throughly tested for timing requirements and for performance quality using test routines in conjunction with a Beckman GC-2A gas chromatograph with a thermal conductivity detector.
- A first-order digital filter was implemented for noise filtering of both the gas chromatograph detector signal and for the column heater control algorithm.
- The noise reduction of the detector input was achieved by reading the amplified detector signal n (typically 3 < n < 5) times in succession and then using the weighted mean (1) where f. -1 , as the input for analysis and control calculations.
- 1 . Noise filtering of the columri heater temperature was achieved with filter state equation, where the gain, f 1 , was given the value 0.7.
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