Unproper Belt Scale Results?

Belt Weighing

Unproper Belt Scale Results?

10 reasons, why your perfect belt scale might under-perform
Belt weighing is common practice in lots of bulk solid handling operations. Although it’s a long established technology, there are still bits and pieces regarding installation and maintenance which might lead to erroneous results. Following you can find the reasons why.
(ed. wgeisler - 31/3/2017)
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Installation of a Milltronics MMI belt scale and Sitrans WS300 speed sensor

It might be a fruit farmer installing a belt scale on a large incline, a salt miner placing an idler too low under a conveyer belt or a cement producer not using a speed sensor.

In each of these scenarios – and countless others – the purchasers of belt scales may be unaware that no matter how sophisticated and capable their scale is, if the location of the equipment isn’t carefully planned, the setup handled properly and numerous other extraneous factors taken into consideration, then the result can be inaccurate weight measurements.

The experts at Siemens – with their decades of experience in the field – not only deliver superior belt scales, but also the know-how to make sure everything is installed properly so you can get the most out of your production equipment. In fact, even if you know you’re going to have an issue that might affect accuracy, they’ll be able to help quantify the extent of the impact so that it can be minimized.

This article looks at 10 of the most common problems you might encounter, and some tips on what you can do so your production is not adversely affected by maintenance or downtime.

The Terminology: Accuracy, Repeatability and Linearity

Before looking at these issues, it’s important to first review the terminology involved, because often the word “accuracy” is used in weighing without really completely understanding it (Fig. 1).

                            Fig. 1: Repeatability and accuracy are both important issues to ensure reliable readings.

Fig. 2: Understanding the proper conveyor terminology will help avoid issues                             
when engineering and installing belt scale applications.                                          

When a belt scale offers one correct measurement, then that measurement is considered accurate. In other words, if 100 tons of material is transported on a conveyor and the scale reads 100 tons, then the accuracy is perfect. But this is just one single data point. Accuracy needs to be repeatable. You need accurate readings over and over and over again. So if 100 tons of material is transported every day for 10 days and the scale tells you 1000 tons have been moved, then that is perfect repeatability.

However, you still need even more than that. What if you have to adjust the load being weighed from its normal amount to a higher or lower weight? For example, your 100 tons per hour most of the time might only be 20 tons per hour on occasion. After such a “turn down,” you still need accuracy and repeatability. If you can achieve that, you now have linearity – the third leg of the measurement stool.

So keep in mind that problems can relate to accuracy, repeatability and linearity – or a combination of any of them.

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