FAQ's

Can CST design and produce a 0.1% Belt Weigher?

Many industries have a need for the highly accurate weighing of bulk materials to a 0.1% standard. When very high tonnages as high as 5,000 to 10,000 tonnes per hour of valuable bulk materials are involved, conventional static methods of weighing become impractical. Truck weigh bridges and even automatic bin scales are some of the available static weighing technologies available however, these are high cost, high maintenance methods. There is a real need for a reliable 0.1% in motion belt weighing system. CST has a strong focus on and commitment to precision belt weighing and is capable of providing 0.1% belt weighing equipment to meet this challenge.

CST, together with our Canadian Agent, TD Micronic of Surrey, British Columbia have supplied a 0.1% belt weighing system to Vancouver Wharves and this equipment is now approved by Measurement Canada as a 0.1% weighing system. The approval number is AM-5612.

Vanncouver Wharves is a British Columbia Rail (BCR) owned facility which exports copper and copper-gold concentrate via ship among other products and they needed a 0.1% belt weighing system to monitor the export of this valuable material. The belt weigher was required to replace an aging automatic bin scale system. Under Canadian law, only ‘cheap materials’ can be legally weighed over a 0.5% weighing system, expensive materials must be weighed over a 0.1% certified system. Since the Copper-Gold concentrate has a value in the order of $1000 or more per tonne it is deemed an expensive material and hence the need for a 0.1% system. Of course the need for a 0.1% system could be justified for any large transaction since 0.1% is still $1,000 per $1,000,000. Even for low cost materials, a million dollars worth of dirt still costs one million dollars!

The equipment is installed on a 1050mm wide belt sloped at 8 degrees from the horizontal running at 2.8m/s and carrying a maximum of 1200 tph of copper-gold concentrate. Under Canadian Weights and measures law, the equipment had to be tested with three by 200 tonne test loads at a flow rate between 70% and 100% of full scale and the maximum allowable error had to be less than 0.07%, or in practical terms, less than 140kg and at the densties involved this is less than 100 litres of material. The most difficult problem in the testing was the management of the material. When, finally, all the material which had been pre-weighed was accounted for, the equipment easily passed the tests even though it had not ben adjusted for over 12 months.

INTERNATIONAL WEIGHTS AND MEASURES AUTHORITIES AND STANDARDS

The requirements of weights and measures authorities around the world vary quite a lot. In Australia we closely follow the European Union which produce documents through the OIML (Organisation International Metrology Legale) based in France. The OIML has produced recommendations R50 and R51 which are the basis of belt weighing in Europe and also by adoption, in Australia. In the USA, the NIST (National Institute of Standards and Technology) produce Handbook 44 which has grown up independently but which is becoming more and more influenced by OIML R50, they also approved wei. The USA has also approved in motion weighing instruments for trade use via their National Type Evaluation System (NTEP). In Canada, the regulations have also been developed independently however they are more similar to the US NTEP system than to OIML.

The interesting difference between the OIML and the other standards is that OIML requires test loads over a range of flow rates while MC and NTEP only require testing at full scale. As a result, the MC test which requires three test loads at or near full scale flow at 0.1% accuracy and the NTEP 0.25% test which also requires three test loads at or near 100% flow are not as rigorous as the OIML 0.25% tests which require that the accuracy be met at 100%, 50% and 20% of full scale flow. The 0.25% test at 20% of full scale is the same as requiring 0.05% of full scale accuracy from the system. CST have many belt weighers trade certified to 0.25% (OIML Class 0.5) in Australia.

CST along with our Canadian agent, TD Micronic are committed to the design and manufacture of 0.1% belt scale systems. We are prepared to supply OIML Class 0.2% systems in fact which will meet the 0.1% accuracy requirement right down to 20% of full scale flow rate. CST are working toward the acceptance of Class 0.2 belt scale system by OIML and we are already confident that we can design and build such systems. We achieve reliable 0.1% systems by designing each of the elements, the weigh frame, the idler sets, the loadcells systems, the electronics systems and the tachometer systems to high precision standards. In addition to this we, together with our Canadian Agents, TD Micronic, have developed some unique systems to keep the equipment running at the required level of precision. For example, our tachometer system is not only available as a dual redundant system but can be made self-checking so that it will adjust its meters per pulse calibration to take out the effects of tachometer pulley wear or buildup. Together with TD Micronic, CST are committed to producing the most accurate belt weighers in the world.

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