A brief description of the operating principles of the infrared IRD-2 Water Vapor Diffusometer and a detailed description of the gravimetric calibration procedure for it is given.
The calibration is achieved by absorbing and weighing the water transmitted by a film installed in the IRD-2 during a measured time interval. The procedure yielded four replicates near the 0.5 g/100 in.2, 24 h rate with 95 percent confidence limits of ±10 percent of the average rate.
The data allowed calculation of the background relative humidity in the IRD-2 dry chamber and the increase in relative humidity per cycle. The background humidity varies with the transmission rate of the film being measured, the dry air flow rate, and the efficiency of drying, but relative humidities near 0.2 percent are indicated with flow rates near 2 ft3/h and transmission rates near 0.5 g/100 in.2, 24 h. The increase in humidity per cycle may vary slightly from instrument to instrument. The instrument used in this study exhibited 0.45, 1.04, and 2.84 percent, respectively, on ranges 5, 4, and 3.
The round robin proved the calibration procedure was accurate and that the IRD-2 yields the same results as ASTM Method E 96 with improved precision.