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ABSTRACT

A calibration procedure for the Sina-scope hygrometer is described. Four saturated salt solutions, covering a range from 0.755–0.967aw, and two foods, with a, levels in the intermediate moisture food range, were tested to determine the accuracy and precision of the Sina instrument. Accuracy, relative to averaged published a, levels for the four standard salts, was evaluated. Most measured values were slightly less than the averaged standards. The greatest difference noted was -1.06% of the standard. Estimates of instrument precision showed that the coefficient of variation decreased with measurement of successively higher a, standard solutions and did not exceed 1%. Instrument readings to two decimal places possessed standard deviations slightly lower than corresponding readings estimated to three decimal places. Standard deviations (20 replicates at each aw) ranged from o—0.004. Estimates of pooled, between-sensor standard deviation showed that there were no significant differences between the two sensors used in those studies. Equilibration periods of 45 or 60 min were almost equally precise. The number of replicates required to produce a given level of data confidence are calculated and presented. Similar results relative to estimates of precision were obtained with the two foods tested.