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Why does your perfect belt scaleunder-perform?

27 October 2016

Here are 10 most common reasons and what you can do about them

It might be a fruit farmer installing a belt scale on a large incline, or 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 set up handled properly, and numerous other extraneous factors taken into consideration, the result can be inaccurate weight measurements.

The experts at Siemens – with their decades of experience in the field – can deliver not only superior belt scales, but the know-how to make sure everything is put in place properly so you can get the most out of your 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 the potential impacts 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 operations are not adversely affected by maintenance or downtime.

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

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

Understanding the terminology: accuracy, repeatability and linearity

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

When a belt scale offers one correct measurement, that measurement is considered accurate. In other words, if 100 tons of material is transported on a conveyor and the scale reads 100 tons, the accuracy is perfect. But that 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 1,000 tons have been moved, that’s perfect repeatability.

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Yet 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 one or more of accuracy, repeatability, and linearity.

Determining the impact: every situation is different

You also need to remember there are limits to how precise the quantifying of any one impact can be. Every application is different and will yield different results.

And most importantly, because a belt scale is part of a larger dynamic application – truly the definition of some- thing with lots of moving parts – most often several of the problems are occurring at the same time. That makes estimating an exact impact extremely difficult. So in addressing the 10 problems outlined in this article, note that each estimated impact is based on an individual issue being looked at in isolation. In reality, it’s likely that multiple issues are involved.

In addition, all the estimates provided are not based on empirical data. They come from the real-world experience of Siemens people. Even though that experience is extensive, any numbers provided should be viewed only as an approximate guide.

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