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How Digital Scales Work

You're Gonna Carry That Weight

Research, industry and commerce require the capacity to measure weights under a seemingly limitless variety of environmental conditions and space constraints, while also controlling for possible errors. So, although strain gauges are the most widely used type of load cell, they're far from the only design in use today [sources: Eilersen; Omega].

Industries that require greater safety and sterility often turn to pneumatic load cells, which derive the weight of an object by measuring the air pressure necessary to balance it. These blowhards work well in the food industry or within hazardous sites because they don't contain fluids that might seep, drip or spurt into the environment. Pneumatic cells can heft a wide range of weights with high accuracy, but they require a clean, dry atmosphere and tend to take their sweet time responding [source: Omega].

Hydraulic load cells, which measure load as a change in fluid pressure, are commonly found weighing tanks, bins and hoppers. Because they function sans electricity, hydraulic cells work well in out-of-the-way locales where power is an iffy prospect. Pricey and complicated but rugged, these fluid-filled gadgets don't flag or fail, even under million-pound loads [sources: Eilersen; Omega; Takhirov et al.].

The terms "strain gauge," "pneumatic" and "hydraulic" describe operating principles -- essentially, the physical laws governing each weighing technique. But a buyer looking for a scale might also consider a cell's size, shape, configuration, materials and other physical aspects based on the job requirements involved. For example, a customer who needs to take measurements in a wet environment might choose a hermetically sealed canister cell, whereas a facility concerned with clearance issues might opt for a thinner bending beam cell [sources: Mashaney; Omega].

Form factors are also chosen for their ability to minimize the effects of extraneous forces. Scales typically measure force along a single direction called the principal axis -- which, in the case of weight, means downward (in the direction of gravitational pull). Weighing errors arise mainly from off-axis forces, which act parallel to the load, and from sideloads, which act perpendicular to it [source: Novatech]. Thanks to their zigzag design, s-beam load cells excel at eliminating sideload [source: Omega].

Within each of these categories and subcategories, there are sizes, shapes and price ranges to fit just about every need imaginable. But there's more to scales than just weighing your options. Measuring force is as fraught with technical troubles as any precision measurement -- no minor matter, when one considers that human lives -- and piles of money -- can rest on the difference of a few grams.