In a sense, it's like a balance scale for electrical resistance: The "weight" resistance on one side tells you the unknown "weight" resistance on the other [sources: Craig ; National Instruments ; Pratt]. A given bridge can contain strain gauges. When multiple gauges are used, they're arranged in opposing directions to improve sensitivity and to mitigate temperature effects. Because the resistance change in a strain circuit can be minuscule, the signal often requires amplification [sources: Craig ; National Instruments ; Pratt].
As a load cell measures compressive resistance change, it transmits a signal to the CPU, which converts it into input for a display board, which then shows the result on a digital screen.
This principle remains true whether you use a strain gauge or some other kind of measuring device. Levers are handy for weighing large objects because leverage converts large forces into small ones.
In some large truck scales, such as the pit scales manufactured by Fairbanks, each pound kilogram increment of weight on one part of the lever converts to only 1 pound 0. Thus, the load cell needs to be able to measure only a fraction of the total weight, and the scales can easily handle between 50, and , pounds 22, and 45, kilograms [source: Mashaney ]. 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.
Hooke's law isn't just for weighing produce; it also underlies the operation of one of the smallest force-measuring devices in the world: the atomic force microscope used in biochemistry, biology and materials engineering.
Such microscopes use a micron-scale silicon or silicon nitride cantilever a spring-like beam, supported on only one side to detect nanonewton and piconewton tugs -- forces on the scale of intermolecular attractions [sources: Cumpson et al. An old saying goes that a man with one watch knows what time it is, but a man with two watches is never sure.
Scales must contend with a similar conundrum: If you weigh the same object twice, do you get the same result? Back to Blog. Old balance scales used to use a series of weights to try and make the two sides of the scale level. For example, you would add objects that you knew the weight of until you achieved balance and could work out the weight of your item. However, we are now able to measure weight automatically.
The majority of scales now work by using devices known as load cells to measure how much an object weighs, whether you are using it for medical, industrial or retail purposes. A load cell is a force gauge that is made up of a transducer that is used to create an electrical signal whose magnitude is in direct proportion with the force being measured.
Essentially, when any weight is placed on to a scale, the load cell bends slightly, which causes the electrical signal that runs through the load cell to change.
This signal change is due to the amount of electrical resistance the bending causes to the strain gauge inside the load cell. The signal is then read by an electronic device, often a digital weight indicator, and transformed into a digital weight value. The value is then displayed for reading. Some differences between types of scales and how they work is due to the different types of load cells. Digital scales are either battery operated or use power mains supply in order to function.
There are a few types of load cells, but we'll focus on the strain gauge load cell, as it is often used in weighing devices. A load cell is essentially a sensor sometimes called a transducer. It is a metallic element that's sturdy, yet elastic enough for a load to deform it, with strain gauges on it.
Some weighing instruments use a single load cell, while others have multiple. When a load is placed on the scale, the strain gauge converts the force or pressure exerted by the load onto the load cell into an electronic signal. Once the load is taken off the scale, the load cell reverts back to its original shape. The load cell determines the instrument's capacity; basically, the maximum mass that can be measured before the deformation becomes permanent, which would damage the device.
How does a strain gauge work? When the film is subjected to changes, the electrical conductors change as well. When a load is placed on the load cell, the load cell bends or strains, hence the name , which changes the electrical resistance. The resistance is recorded by the strain gauges. When the load is taken off, the load cells return to their normal shape, and so do the strain gauges. The change in electrical resistance is converted to a digital signal, which is then processed to look readable on the display.
Since a load cell essentially measures mass by converting the deformation caused by the load to an electronic signal, it is sensitive to accidental deformation, such as shocks or temperature changes.
That's why it's essential to treat weighing instruments with care and to calibrate them frequently. Mechanical balances are often triple beam balances like our TBB. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe.
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