Controlling one’s Gold Assets

Weighing Technology

Controlling one’s Gold Assets

A Belt Scale System worth its Weight in Gold
Gold is one of the most important metals in the world – not only for jewelry or gold assets, but also for many industrial applications. For its production in Russia, a company looked for a robust and calibratable scale to control their gold (ore) flow.
(ed. WoMaMarcel - 26/2/2015)
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Although not a scale intended for use in trade or load out, the company required that it meet metrological approvals for the local governing agency. In Russia this is known as GOST Metrological. Siemens is one of the few companies in the world that has this approval for its belt scales.

The Mayskoe site already had a scale installed from a competitor: a full frame four-idler design. Unfortunately, the scale was installed in an area near the drive pulley, which is challenging for accurate weighing performance. The reason was due to its size and the fact that the conveyor is curved, limiting the options for installation based on these constraints.

The four-idler model was reporting an accuracy above 1% and also experienced temperature-related issues. At sub-zero temperatures, the four-idler model would produce a significant error. When the customer investigated the situation, it was identified that the large frame of the four-idler scale had been deformed as a result of the forces due to thermal expansion and contraction. This was causing the load cells to output incorrect signals interpreted as product weight, which falsified the measurement.

Better Accuracy to the Rescue

Siemens offered the Milltronics MMI belt scale, a combination of two or more MSI belt scales in tandem. The compact design of the single idler model facilitated quick and easy installation, and it also reduced the amount of total weighing space required. This allowed a more suitable area in the conveyor to be selected. A Sitrans WS300 speed sensor mounted on a self-cleaning bend pulley, a calibration test chain, and a Milltronics BW500 integrator completed the belt scale system solution from Siemens.

The integrator was connected to the plant network via the optional Profibus DP, which allowed the scale to be completely integrated into the plant automation system. The WS300 speed sensor also features special electrical circuitry, which eliminates false speed sensor signals from vibration. A bushed calibration test chain is a reliable option for calibration when material tests are not possible to help simulate material being transported on the belt. Siemens recommends the use of test chains on trade-approved applications for this reason.

After a fast and smooth installation and commissioning, the belt scale system was put into service. After monitoring the scale, the accuracy obtained was 0.15%, which more than satisfies this company’s needs!

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