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What Is a Spring Scale?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 02 September 2014
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A spring scale is a scale which measures weight by determining the deflection of a spring. As long as the spring in good condition, the spring scale will be reasonably accurate. The big advantage to this type of scale is that it is cheap and very easy to use. The primary disadvantage is that spring scales are not always very accurate, and they are subject to wearing down over time, which causes the scale to register weights incorrectly.

The design of a spring scale takes advantage of the fact that if one knows the distance a spring is extended from a resting state, it is possible to determine the amount of force needed to extend the spring that far. As long as the metal in the spring is not stretched beyond its elasticity, it should give a reasonably accurate reading, which can be registered by the scale in a variety of ways, depending on the design.

Spring scales must be carefully calibrated in order to work properly. The properties of the individual spring in the scale must be known by the manufacturer, and the scale needs to be routinely checked to confirm that it is accurate. If the spring is overloaded and worn out, it will skew the scale results, creating an inaccurate reading. The spring can also break, causing the scale to fail altogether.

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A classic example of a spring scale can be found in the produce sections of many supermarkets. With this type of scale, people put objects into a tray held below the spring scale, and the weight of the objects causes the spring to expand. The scale's dial reflects the amount of deflection experienced by the spring, indicating how much force was exerted on the spring to cause it to move. Spring scales are used in many settings where people need to quickly weigh things, and pinpoint accuracy is not necessarily needed.

Several companies sell portable spring scales with hooks which can be tremendously useful. To use such a scale, the scale is hung from a fixed object, and the object being weighed is attached to the hook. This lightweight scale design is useful for people doing field work, as it allows them to weigh objects in the field without needing to carry around a large scale. These small spring scales are also sometimes used in the classroom to educate children about weights and measures, and to introduce students to the basic properties of springs.

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anon299008
Post 5

I have a spring scale that reads up to 12 kg. The force I want to measure is only about 0.4 kg. Seems too small for the scale, to be accurate.

So, for the best accuracy, how much of the scale should the item you are measuring take up? Over 25 percent? Over 50 percent?

David09
Post 4

@miriam98 - I think any spring scale balance used in a commercial setting would have to be accurate. I doubt that the retailers would try to pull one over on us, just for a few extra pennies on a pound of potatoes, while risking having their whole operation shut down by an inspector.

I don’t know that inspectors check the scales, but I’d think that there would have to be some quality control standards somewhere.

miriam98
Post 3

@hamje32 - Everyone would like to know how accurate those bathroom scales are; weight is such a touchy subject after all.

If we see we’ve lost a few pounds, we want to know that it’s real and not imagined. Frankly, I am more concerned about the accuracy of the hanging scales in the supermarket when I go to buy produce.

How do we know that these are accurate? The grocers stand to make a little extra profit by tweaking those things, just a little here and there.

Mammmood
Post 2

@hamje32 - I think your explanation of a spring weight scale is correct. Whether the spring is compressed or stretched the concept is the same.

As for a digital scale, if it’s a digital scale that still relies on a spring-as I assume most of them do-then I don’t think that the digital component would give you an extra notch of accuracy. It would, in my opinion, just make the scale easier to read.

I do realize, however, that a digital scale would certainly give an illusion of being more accurate, but I don’t think it would be, so long as you were still using a spring.

hamje32
Post 1

I take it then that typical bathroom balance scales operate by the same mechanism and principle, except that in this case the deflection would be inward and not outward.

That is to say, I think the spring would be compressed and not stretched. With the explanation given, I would suppose that you take the resting position of the spring, then measure its final position when it is compressed, and use that ratio to determine the amount of applied force.

I’m not a genius to have figured this out, but it seems to follow logically from the explanation in this article. I would be open to correction, however.

More importantly, however, I’d love to know if a digital spring scale is anymore accurate than one that is not digital?

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