Gy's Formula
Hi Kmukuku,
I understand Gy's sampling formula and constant, and prefer to ignore both. Start working with the interleaved sampling protocol, which gives a realistic estimate for the sum of the variances for the primary sample selection, sample preparation and analytical stages. This protocol is incorporated in several ISO Standards, including those developed by ISO TC69-Applications of Statistical Methods.
It is based on partitioning a set of primary increments into a pair of interleaved subsets such that one consists of all odd-numbered increments (A-primary sample in ISO parlance), and the other of all even-numbered increments (B-primary sample). A pair of interleaved primary samples gives a single degree of freedom for a tabulated value of t0.05;1=12.706 but five (5) pairs give a tabulated value of t0.05;5=2.571 wheras a typical monthly production period gives a value of close to t0.05;30=2.04.
Posted on my website is a paper titled 'Sampling in Mineral Processing', which describes interleaved sampling and gives the formula for the variance of Gy's sampling constant. Under 'Templates' you'll find an Excel file that gives confidence limits for monthly PGM production. Let me know how it works for your chromite.
Kind regards,
Jan W Merks ■
Gy's formula
i dont understand how you practically obtain the sampling constant and the variance, in as far as the gy's formula is concerned. i am a recent graduate and i am trying to set up a sampling system on an ore heap as the chromite ore arrives to the plant.the challenge is to try to devise a system that will be more accurate and still affordable to implement. this is the same also for the belt cut, that is how i stumbled upon gy's formula, and i am trying to see if it is applicable in any of my two cases. ■