The technique of producing reference-standard gas by the flow-measuring method

Abstract

The reference-standard gas-generating system used for the calibration of an air-pollution measuring instrument is described. By blending the pollutant gas and the diluent gas of known flow rates, the system can produce the mixed gas continuously. The concentration of the pollutant in the mixed gas is given as the ratio of the flow rates of each gas. The system is composed of a capillary flowmeter for the pollutant gas, a laminar flowmeter for the diluent gas and a mixing element. These componenta are placed in a constant-temperature bath. The following experiments on the problems of producing the standard gas were made: 1. (1) Calibration of the flowmeter by sonic nozzle. 2. (2) Verification of homogeneity of mixed gas. 3. (3) Comparison with the standard gas (in cylinder) prepared by the mass-measuring method. The system makes possible production of mixed gases, of concentration from 0.1 to 1000 ppm for the pollutant gas (CO and NO) and with a stability of ±0.3%, during 24 h.