What components are needed to make a good quality weighing scale – Load Cells & Strain Gauges

There are several components needed to make a good quality weighing scale.
In this article I talk about load cells and strain gauges, how they work and important points to consider.

The load cell is one of the most important components in a weighing scale, when coupled with a digital indicator it dictates how well the scale will perform. Many low cost scales use cheaper load cells, understanding the quality of a load cell can be difficult.

The main component of a load cell is a strain gauge. Strain gauges are made up of an insulated flexible backing which holds a metallic foil pattern. The gauge is attached to a load cell by adhesive. As the load cell is deflected (by adding weight), the foil deforms, causing its electrical resistance to change. This electrical change is interpreted as a weigh value on the digital display.

Strain gauges are susceptible to exterior factors such as moisture and temperature, lower cost load cells may not be as well protected against these elements causing the units to develop errors or fail sooner.

Load cells help determine the following characteristics of a weighing scale:

Linearity:
Load cells may feature hysteresis style errors shown in the graph, the desired results is a straight line at 45 degrees this is the linearity. The increasing and decreasing load applied is displayed in a linear fashion.

Linearity of a Load Cell

Accuracy:
This is the area that covers the difference between a reference and the value displayed on the weighing terminal. High accuracy scales can display weight readings to high resolutions and stay close to the reference value, for example a high accuracy load cell may be able to display 10Kg as 10.0000Kg, a lesser load cell may only manage 10.0020kg, it may also fluctuate and not be stable.

Accuracy of a weighing scale

Repeatability:
Repeatability is the measurement in variation taken by a loading a scale with the same weight under the same conditions. A scale may be said to be repeatable when it produces the same measurements accurately with a defined mass.

Eccentricity:
Single point load cells may perform differently when loads are applied in different places. A high quality load cell will be able to display off centre loads accurately where as a lower cost cell may struggle to give accurate results. For example results for sections 1/2/3/4 maybe the same on higher quality load cells, results for lower quality ones may vary from point to point.

Eccentric loading of a weighing scale

When buying a cheap scale it’s worth considering its components and how they affect your results.

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