How Do Scales Measure Weight?

the pharmaceutical bench. From the smallest, most fine tuned laboratory balance to the pit and girder monsters that weigh train cars and tractor trailers, scales make modern life possible. Scales, or more specifically, balances weighed heavily on the minds of ancient builders, inventors, and economic advisors. Too. Small balance weights dating back to around five to six thousand years ago provide some of the first hints of mankind evolving grasp

of science and mathematics. The most basic surviving balance from Egypt predates the Dynastic period, placing its construction at earlier than three thousand BCE. Like us, the ancient Egyptians applied scales both in trade and in a saying ores and alloys balances way an object by matching it against one or more reference weights. They have a delicate touch and

are still used in laboratories. Scales use somewhat different physical principles and mechanical components to measure weight in other forces. Spring scales, for example, measure weight using Hook's law, by which you can relate in objects weight to the stretching or compression of a spring made from a given material.

Not all scales use springs, but all do measure weight using mechanical components, So mechanical and digital scales differ only in how they display that weight, mechanically like with a needle on a dial, for example, or electronically alike with an LED display. In a latter case, the scale employs an analog to digital converter that translates the continuous readout data from the scale into discrete digital information, much in the same way that an MP three encoding scheme digitizes

the waveforms of music. An internal CPU converts the data into input for a display board, which then shows the result on a digital screen. Generally speaking, digital scales require less expertise to use than those with mechanical readouts and are capable of higher precision and faster processing. Still, the capabilities of specific devices vary, particularly when the weights are measured in tons. But let's talk more about those different

mechanical components that let us measure weight with scales. Think of how a roadside carjack might lift a car via mechanical adage the leverage of a handle or the inclined plane of a screw, or how a car mechanic's hoist might use hydraulic pressure in the same way. Different types of scales weigh objects using a variety of operational principles, like hydraulics, pneumatics, or bending beans. Scales come in all shapes, sizes, and configurations, but the basic component doing the measuring is

nearly always a load cell. A load cell is a kind of transducer, which is a term for a device that converts one form of energy into another. Through load cells, digital scales change mechanical energy the smooshing caused by a sitting load or the stretching caused by a hanging load, into an electrical effect. The widely used strain gage, for example, reads compression or tension as tiny changes in electrical resistance in what's called a whitstone bridge. Let's break that down

using a compression strain gauge as an example. Okay, Compression occurs when an applied force reduces an object's volume, but it can also refer to a more general decrease in size along one or more dimensions. As it happens, squishing, an electrically conductive material changes its electrical resistance because longer and narrower wires are more electrically resistant than shorter and wider wires. Think of it like water pumping through a pipe.

The longer and narrower the pipe, the harder it will be to force water through it. Now, different materials experience different changes in resistance during compression, a quality known as gauge factor. A gauge factor can also alter in response to temperature. The go to material for strain measurements is called constantine alloy. It's usually fifty five percent copper and forty five percent nickel, and it performs well at the

range temperatures that humans are comfortable at. To detect the change in resistance caused by weight compression, one or more strain gages are placed within what's called a whitstone bridge. A whitstone bridge is an electrical circuit that can detect an unknown electrical resistance by balancing it against known resistances elsewhere in the circuit. In a sense, it's like a balance scale for electrical resistance. The weight of the resistance on one side tells you the unknown weight of the

resistance on the other. Strain gauges are the most widely used type of load cell, but they're not the only one. After all, 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. Industries that require greater safety and sterility often turn into 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 and at hazardous sites because they don't contain fluids that might seep, drip, or spurt into the environment. Pneumatic cells can have a wide range of weights with high accuracy, but they require a clean, dry atmosphere and tend to take their sweet time responding Hydraulic load cells, which measure load as a change in fluid pressure are commonly found weighing tanks, bins, and hoppers.

Because they function without electricity, Hydraulic cells work well in out of the way locals where power is a ify prospect. They're pricey and complicated, but rugged they can handle million pound loads. Load cells also come in all kinds of different sizes, shapes, configurations, and materials, so that you can use scales in different environments for different jobs. If you need to take measurements in a wet environment, you can

opt for a hermetically sealed canister cell. If you're in a facility concerned with height clearance issues, you can use a thinner bending beam cell. And if you're expecting to deal with extraneous forces affecting the load cell, say you're using scales in a moving vehicle, in deep water or on an aircraft, an s beam load cell that uses

a zigzag design can help control for that. Measuring force is as fraught with technical troubles as any precision measurement, which is no minor matter when one considers that piles of money, and more importantly, human lives can rest on the difference of a few grams. Researchers develop all kinds of technologies to help make scales dependable in real world circumstances.

No matter the well scale, these devices could range from being accurate in laboratory settings to highway weight enforcement and beyond. On the larger end, scales employ levers to convert extra large forces into manageable ones. Thus, the load cells in some large truck scales only need to be able to measure a fraction of the total weight, and thus can easily handle between fifty to one hundred thousand pounds, which is around twenty five to forty five thousand kilos, which

is a lot either way. And remember how Hook's law helps you more or less accurately weigh your fruit and vegetables on the spring scale at the grocery store. 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, which is a spring like beam supported only on one side to detect nano Neewton and peak Newton tugs forces on the scale of intermolecular attractions. Today's episode is based on the article how digital scales work on HowStuffWorks dot Com, written by Nicholas Jerbis. Brain Stuff is production of by Heart Radio in partnership with HowStuffWorks dot Com and is produced by

Tyler Klang. For more podcasts from my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.