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Being able to accurately measure the weight of objects is critical in personal and industrial uses. From medicine and health, to pharmaceutical manufacture, freight movement, and every other form of manufacturing, accurate weighing is central to success in all these fields. Therefore scales and weight measurement touches every part of our lives.

‘Weight’ is a relative measure. If you were to weigh an object on earth and then weigh it again on a planet with a different gravity, you would experience a totally different weight on the scale you are using. In one way, this makes it easy to understand the original scale which was a balance system. The object being weighed was put on a pan on one side of the pivot of a scale and objects with a known weight were put on the opposite pan of the balance scale until they two pans equalised and ‘balanced’ – thereby showing the unknown weight of the object.

Types of Scales

Spring scales have a rigid structure connected to a stretched or compressed spring and the object to be weighed can be attached to an end with a marker to denote the weight increments. As the object is weighed, the spring is either stretched or compressed. The spring has a know elasticity (see Hooke’s law) or, has a measure of how much the spring will extend or contract based on the amount of force applied to it. This known measure takes into account gravity. The same principle applies to simple bathroom scales, in this case, the spring is compressed. The disadvantage to these is they can be inaccurate. They work on the principle of what gravitational force the object is being subjected to. Thus it can also be inaccurate based on local gravity conditions, the error margin can be up to 0.5% in different regions.

Strain gauge scales are electronic and measure the strain or deflection produced by the beam weighing the object of unknown weight. The strain is sometimes across a spring or conductive foil. It is the changes in resistance that determine the weight measured. They are seen in weighbridge applications and can very successful for weighing very heavy loads.

Hydraulic scales tend to measure heavy weights and are used in most industrial scenarios. The method of weighing is based on liquid displacement which can convert a pressure signal into an electrical signal. Hydraulic scales are often seen as onboard weighing systems as they are highly accurate and are designed for industrial use.

Electronic or digital scales can measure miniscule changes in resistance across a metal foil of some description. A load cell is the sensor and it uses a strain gauge. There is a backing board which has some metal foil bonded onto a printed circuit board or other backing. As the object is weighed, the backing is flexed, which in turn strains the metal foil. This causes small changes in resistance which can be measured. It is extremely good at measuring very small changes in mass and can be seen in personal weighing as well as a plethora or other weighing situations.

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