VARIANCE OF AVERAGE STREAM COMPOSITIONS OBTAINED BY AUTOMATIC INCREMENTAL SAMPLING

Mean values of stream compositions in mineral processing plants are fr equently estimated by the analysis of a composite sample. This sample is the result of an accumulation of material increments extracted at s ystematic time intervals. The measurement error which is evaluated in this study is the difference between the sample composition and the tr ue composition of the total material which flows during the time perio d of increment accumulation. The error variance is calculated assuming that the species flowrate random variations are described by their va riances and autocorrelation functions. The error is decomposed into tw o contributions: the discretization error and the sampling error. The results are compared to those of Gy's theory of particulate material s ampling. This estimation of the measurement error variance is essentia l for the application of data reconciliation or filtering techniques, for gross error detection, and for the estimation of process performan ce indicator reliability.