Finding a Reliable Way of Valuing a Stockpile
"Equipment suppliers are often frustrated by clients who place price above all else. One such supplier, Ian Burrell of Control Systems Technology, submitted this commentary to stress the importance of looking at price in the context of overall performance. His comment is echoed increasingly these days by suppliers of all equipment - not merely belt weighers. Hopefully this comments will get through to those equipment purchases who put short term gain above long term performance"
Belt weighers are often relied upon to establish the balance sheet value of mine stockpiles. The "bean counters" of this world rely heavily upon belt weighers as an essential piece of equipment critical to plant management.. However, at the purchasing end of the spectrum, there is often a very unhelpful 'cheapest possible' approach because of the shortsighted desire to maximise the project's financial yield of capital invested. This is often found to be 'penny wise' and 'pound foolish'.
The best belt weighers in the market can cost from five to ten times the cost of the industry standard . Some of these supposedly '0.5 percent' belt weighers have a single weigh idler and cost well under $10,000. However, it is interesting to note that none of these cheaper units are certified for trade use in Australia. Trade-certified (ANSC pattern approved) belt weighers are usually four idler four load cell units which cost considerably more than the single idler 'nominal' +-0.5 percent units. Control Systems Technology (CST) belt weighers, trade certified to +-0.5$ on the day of initial verification, perform, for the majority of their operating life, with errors in the order of +-0.15 percent. they rarely stray outside the +/-0.5 percent verification error limit and would not be expected to have anywhere near +/-1.0 percent error in any normal circumstance.
This is not necessarily the case with some other makes of +-0.5 percent belt weighers, some of which are lucky to be within promised accuracy at all and are often reported with a 5 percent error.
There are compelling practical reasons for purchasing higher quality and higher cost belt weighers. Consider the hypothetical case of a facility with 1 million tpa production. The stockpile, which might be 50,000t, is only 5 percent of this annual production. The stockpile necessarily contains the sum of the total belt weigher error for the year.
How accurately, would you like to value a 2.5 million dollar asset? Is an error of +/-10 percent good enough for your company? Because that is what an accuracy of 0.5 percent of 5 percent represents. Probably this is not good enough, so it can make sense to invest the extra money to achieve an in service accuracy of less than 0.25%. CST have a range of Australian developed precision belt weighers which have genuine in-service accuracies of +/-0.5% and +/-0.25%.
By Ian Burrell, Control Systems Technology Pty. Ltd.
Australian Bulk Handling Review - April/May 2001