Wednesday, May 25, 2011

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Analog weight Scale

The most common weight-scale implementation is to use a  transducer bridge, with voltage output directly proportional to the weight placed on it. The trend in weight scales towards higher accuracy and lower cost has produced an increased demand for high-performance analog signal processing at low cost.By connecting a strain Gage in the bridge ,the differential instrumentation amplifier can be converted in to a simple analog weight scale.

 In the analog weight scale, strain Gage elements are connected in all four arms of the bridge. The elements are mounted on the base of the weight platform, so that, when an external force or weight is applied to the platform, one pair of elements in the opposite arms elongates, whereas the other pair of elements in the opposite arms compresses.

 On the other hand, When no weight is placed on the platform, the bridge is unbalanced, RT1=RT2=RT3=RT4=R, and the output voltage of the weight scale can be zero. When a weight is placed on the scale platform, the bridge becomes unbalanced. In other words, when the weight is placed on the platform, RT1 and RT3 both decrease in resistance and RT2 and RT4 both increase in resistance (Figure 01).
The analog weighing measuring scales need to be hung properly before we start measuring anything using the same. They never allow measuring the weight of anything that we want as they have some limitations. If we think about measuring anything using an analog scale we need to check the analog lines to get the nearby accurate measurement.

One thing we need to keep in our mind while using such a scale is the limitation, if we load anything which weights more than the mentioned limit by the manufacturer of the scale we may end up damaging the same. Analog scales were never capable of providing accurate weight of any item and at the same time, it involves human effort to measure anything where the chances of human error are quite normal

For better accuracy, a microprocessor-based digital weight scale may be constructed.But it is much more complex and expensive than the analog scale.

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