| There are several components needed to make a | | | | decreasing load applied is displayed in a linear fashion |
| good quality weighing scale. In this article I talk about | | | | Accuracy: |
| loadcells and strain gauges, how they work and | | | | This is the area that covers the difference between |
| important points to consider. | | | | a reference and the value displayed on the weighing |
| The load cell is one of the most important | | | | terminal. High accuracy scales can display weight |
| components in a weighing scale, when coupled with a | | | | readings to high resolutions and stay close to the |
| digital indicator it dictates how well the scale will | | | | reference value, for example a high accuracy load cell |
| perform. Many low cost scales use cheaper load cells, | | | | may be able to display 10Kg as 10.0000Kg, a lesser |
| understanding the quality of a load cell can be difficult. | | | | load cell may only manage 10.0020kg, it may also |
| The main component of a load cell is a strain gauge. | | | | fluctuate and not be stable. |
| Strain gauges are made up of an insulated flexible | | | | Repeatability: |
| backing which holds a metallic foil pattern. The gauge | | | | Repeatability is the measurement in variation taken |
| is attached to a load cell by adhesive. As the load cell | | | | by a loading a scale with the same weight under the |
| is deflected (by adding weight), the foil deforms, | | | | same conditions. A scale may be said to be |
| causing its electrical resistance to change. This | | | | repeatable when it produces the same |
| electrical change is interpreted as a weigh value on | | | | measurements accurately with a defined mass. |
| the digital display. | | | | Eccentricity: |
| Strain gauges are susceptible to exterior factors such | | | | Single point loadcells may perform differently when |
| as moisture and temperature, lower cost loadcells | | | | loads are applied in different places. A high quality |
| may not be as well protected against these elements | | | | loadcell will be able to display off centre loads |
| causing the units to develop errors or fail sooner. | | | | accurately where as a lower cost cell may struggle |
| Loadcells help determine the following characteristics | | | | to give accurate results. For example results for |
| of a weighing scale: | | | | sections 1/2/3/4 maybe the same on higher quality |
| Linearity: | | | | load cells, results for lower quality ones may vary |
| Loadcells may feature hysteresis style errors shown | | | | from point to point. |
| in the graph, the desired results is a straight line at 45 | | | | When buying a cheap scale it's worth considering its |
| degrees this is the linearity. The increasing and | | | | components and how they affect your results. |