Patent ID: 6010243
Filing Date: 2000-01-04
Classification: C12M,G01N,Y10T

Abstract:
A method of zero-point adjustment of a thermal conductivity detector cell sensor system having thermal conductivity detector cells, including a measuring cell, connected to control the atmosphere within a chamber, in which the atmosphere contains CO.sub.2,comprising the steps ofin a first phase:(a) opening the chamber to ambient atmosphere;(b) closing the chamber and isolating the chamber with respect to ambient atmosphere and any other external gas sources;in a second phase:(c) establishing a first timing interval;(d) establishing a CO.sub.2 tolerance band within a predetermined tolerance range for measured CO.sub.2 % concentration values;(e-1) at the expiration of said first timing interval, carrying out a measurement of CO.sub.2 by said measuring cell, and(e-2) if a deviation from zero is detected, resetting the CO.sub.2 value to zero, repeating steps (c) through (e-1) until the CO.sub.2 value is within the tolerance band, and storing said deviation, within the tolerance band, to obtain a CO.sub.2 zero-point correction offset value;(f) introducing water vapor into said chamber;in a third phase:(g-1) establishing a second timing interval;(g-2) at the expiration of said second timing interval, carrying out a measurement of CO.sub.2 by said measuring cell, and(h) if a deviation from zero is detected, resetting the CO.sub.2 value to zero, repeating steps (g-1) and (g-2) until the measured CO.sub.2 value remains within said tolerance band during at least a major portion of said second timing interval, to thereby obtain a humidity-CO.sub.2 offset value;(i) utilizing said humidity-CO.sub.2 zero-point offset value to modify, if necessary, the CO.sub.2 zero-point correction offset value;(j) determining a calibration limit range;(k-1) if the calibration limit range has not been exceeded, indicating the zero-point offset value of the CO.sub.2 measurement, based on the CO.sub.2 offset value and the humidity-CO.sub.2 value, terminating the zero-point adjustment procedure and admitting gas into the chamber;(k-2) if the calibration limit range has been exceeded, providing an error display and, optionally, resetting the calibration range limit of step (j) and then repeating steps (a) through (k-1) or (k-2).