SAMPLING OF AUTOCORRELATING POWDER FLOWS

Sampling powder flows in industrial grinding circuits are discussed. W ork was done with different types of sampler and with different minera ls and sampling objectives. It was found that all the samplers showed marked autocorrelation in sample mass for all the minerals ground. Typ ical autocorrelation could be found at both high (1 . 10(-3) - 15 . 10 (-3) Hz) and low (1 . 10(-4) - 4 . 10(-4) Hz) frequencies. Higher freq uencies were attributed to powder transport and low frequencies to mil l circuit variations. The effects of the found autocorrelation on syst ematic errors and on industrial sampling schemes are discussed. System atic sampling produced large errors if operated at sampling intervals that were high-frequency autocorrelation frequencies or small multiple s of these. Low-frequency autocorrelation was less detrimental to the sampling results.