Computer Data Processing
Contemporary chromatographs will include a dedicated computer. which controls the operation of the chromatograph. In large analytical laboratories, chromatographic data acquisition and processing for a number of different instruments, can be handled by a central computer. Central computers can time-share with a number of chromatographs and can provide laboratory housekeeping functions, such as monitoring the progress of samples through the laboratory from admission to the final report. Data processing can be logically divided into two stages; firstly the analog data is converted into digital form, acquired and stored in an appropriate memory; secondly, the digital data is recalled, processed and the results reported in a chosen format.
The Acquisition of Chromatography Data
A diagram showing the individual steps involved in acquiring and processing chromatography data is shown in figure 35. After processing the sensor output, the analog signal then passes to a scaling amplifier and then to an analog-to-digital converter (A/D). The digital signal from the A/D converter, passes, via an appropriate interface, to the computer and is then stored in memory. In real time, or
at the end of the analysis, the computer recalls the data, carries out the necessary calculations and displays the result on a monitor and/or printer.
Figure 35. A Block Diagram of a Typical Chromatography Data Acquisition System
Detectors outputs range from 0 to 10 mV, whereas the necessary input to most A/D converters is much greater (viz 0 to 1.0 V). Thus, an instantaneous measurement of 2 mV from the detector must be scaled up to 0.2 volt by a linear scaling amplifier.
Figure 36. Stages of Data Acquisition
