Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff,
Speaker 1: Lauren Bogelbaum. Here, there's something so commonplace about a weighing
Speaker 1: device that it's easy to forget its deeper significance, as
Speaker 1: these slightly skewed spring scale in any local produce aisle
Speaker 1: reminds us. The scale has long served humans as the
Speaker 1: chief arbiter of commerce, the maker or breaker of shipping
Speaker 1: budgets and carry on capacity, and the utility player of
Speaker 1: the pharmaceutical bench. From the smallest, most fine tuned laboratory
Speaker 1: balance to the pit and girder monsters that weigh train
Speaker 1: cars and tractor trailers, scales make modern life possible. Scales,
Speaker 1: or more specifically, balances weighed heavily on the minds of
Speaker 1: ancient builders, inventors, and economic advisors. Too. Small balance weights
Speaker 1: dating back to around five to six thousand years ago
Speaker 1: provide some of the first hints of mankind evolving grasp
Speaker 1: of science and mathematics. The most basic surviving balance from
Speaker 1: Egypt predates the Dynastic period, placing its construction at earlier
Speaker 1: than three thousand BCE. Like us, the ancient Egyptians applied
Speaker 1: scales both in trade and in a saying ores and
Speaker 1: alloys balances way an object by matching it against one
Speaker 1: or more reference weights. They have a delicate touch and
Speaker 1: are still used in laboratories. Scales use somewhat different physical
Speaker 1: principles and mechanical components to measure weight in other forces.
Speaker 1: Spring scales, for example, measure weight using Hook's law, by
Speaker 1: which you can relate in objects weight to the stretching
Speaker 1: or compression of a spring made from a given material.
Speaker 1: Not all scales use springs, but all do measure weight
Speaker 1: using mechanical components, So mechanical and digital scales differ only
Speaker 1: in how they display that weight, mechanically like with a
Speaker 1: needle on a dial, for example, or electronically alike with
Speaker 1: an LED display. In a latter case, the scale employs
Speaker 1: an analog to digital converter that translates the continuous readout
Speaker 1: data from the scale into discrete digital information, much in
Speaker 1: the same way that an MP three encoding scheme digitizes
Speaker 1: the waveforms of music. An internal CPU converts the data
Speaker 1: into input for a display board, which then shows the
Speaker 1: result on a digital screen. Generally speaking, digital scales require
Speaker 1: less expertise to use than those with mechanical readouts and
Speaker 1: are capable of higher precision and faster processing. Still, the
Speaker 1: capabilities of specific devices vary, particularly when the weights are
Speaker 1: measured in tons. But let's talk more about those different
Speaker 1: mechanical components that let us measure weight with scales. Think
Speaker 1: of how a roadside carjack might lift a car via
Speaker 1: mechanical adage the leverage of a handle or the inclined
Speaker 1: plane of a screw, or how a car mechanic's hoist
Speaker 1: might use hydraulic pressure in the same way. Different types
Speaker 1: of scales weigh objects using a variety of operational principles,
Speaker 1: like hydraulics, pneumatics, or bending beans. Scales come in all shapes, sizes,
Speaker 1: and configurations, but the basic component doing the measuring is
Speaker 1: nearly always a load cell. A load cell is a
Speaker 1: kind of transducer, which is a term for a device
Speaker 1: that converts one form of energy into another. Through load cells,
Speaker 1: digital scales change mechanical energy the smooshing caused by a
Speaker 1: sitting load or the stretching caused by a hanging load,
Speaker 1: into an electrical effect. The widely used strain gage, for example,
Speaker 1: reads compression or tension as tiny changes in electrical resistance
Speaker 1: in what's called a whitstone bridge. Let's break that down
Speaker 1: using a compression strain gauge as an example. Okay, Compression
Speaker 1: occurs when an applied force reduces an object's volume, but
Speaker 1: it can also refer to a more general decrease in
Speaker 1: size along one or more dimensions. As it happens, squishing,
Speaker 1: an electrically conductive material changes its electrical resistance because longer
Speaker 1: and narrower wires are more electrically resistant than shorter and
Speaker 1: wider wires. Think of it like water pumping through a pipe.
Speaker 1: The longer and narrower the pipe, the harder it will
Speaker 1: be to force water through it. Now, different materials experience
Speaker 1: different changes in resistance during compression, a quality known as
Speaker 1: gauge factor. A gauge factor can also alter in response
Speaker 1: to temperature. The go to material for strain measurements is
Speaker 1: called constantine alloy. It's usually fifty five percent copper and
Speaker 1: forty five percent nickel, and it performs well at the
Speaker 1: range temperatures that humans are comfortable at. To detect the
Speaker 1: change in resistance caused by weight compression, one or more
Speaker 1: strain gages are placed within what's called a whitstone bridge.
Speaker 1: A whitstone bridge is an electrical circuit that can detect
Speaker 1: an unknown electrical resistance by balancing it against known resistances
Speaker 1: elsewhere in the circuit. In a sense, it's like a
Speaker 1: balance scale for electrical resistance. The weight of the resistance
Speaker 1: on one side tells you the unknown weight of the
Speaker 1: resistance on the other. Strain gauges are the most widely
Speaker 1: used type of load cell, but they're not the only one.
Speaker 1: After all, research, industry, and commerce require the capacity to
Speaker 1: measure weights under a seemingly limitless variety of environmental conditions
Speaker 1: and space constraints, while also controlling for possible errors. Industries
Speaker 1: that require greater safety and sterility often turn into pneumatic
Speaker 1: load cells, which derive the weight of an object by
Speaker 1: measuring the air pressure necessary to balance it. These blowhards
Speaker 1: work well in the food industry and at hazardous sites
Speaker 1: because they don't contain fluids that might seep, drip, or
Speaker 1: spurt into the environment. Pneumatic cells can have a wide
Speaker 1: range of weights with high accuracy, but they require a clean,
Speaker 1: dry atmosphere and tend to take their sweet time responding
Speaker 1: Hydraulic load cells, which measure load as a change in
Speaker 1: fluid pressure are commonly found weighing tanks, bins, and hoppers.
Speaker 1: Because they function without electricity, Hydraulic cells work well in
Speaker 1: out of the way locals where power is a ify prospect.
Speaker 1: They're pricey and complicated, but rugged they can handle million
Speaker 1: pound loads. Load cells also come in all kinds of
Speaker 1: different sizes, shapes, configurations, and materials, so that you can
Speaker 1: use scales in different environments for different jobs. If you
Speaker 1: need to take measurements in a wet environment, you can
Speaker 1: opt for a hermetically sealed canister cell. If you're in
Speaker 1: a facility concerned with height clearance issues, you can use
Speaker 1: a thinner bending beam cell. And if you're expecting to
Speaker 1: deal with extraneous forces affecting the load cell, say you're
Speaker 1: using scales in a moving vehicle, in deep water or
Speaker 1: on an aircraft, an s beam load cell that uses
Speaker 1: a zigzag design can help control for that. Measuring force
Speaker 1: is as fraught with technical troubles as any precision measurement,
Speaker 1: which is no minor matter when one considers that piles
Speaker 1: of money, and more importantly, human lives can rest on
Speaker 1: the difference of a few grams. Researchers develop all kinds
Speaker 1: of technologies to help make scales dependable in real world circumstances.
Speaker 1: No matter the well scale, these devices could range from
Speaker 1: being accurate in laboratory settings to highway weight enforcement and beyond.
Speaker 1: On the larger end, scales employ levers to convert extra
Speaker 1: large forces into manageable ones. Thus, the load cells in
Speaker 1: some large truck scales only need to be able to
Speaker 1: measure a fraction of the total weight, and thus can
Speaker 1: easily handle between fifty to one hundred thousand pounds, which
Speaker 1: is around twenty five to forty five thousand kilos, which
Speaker 1: is a lot either way. And remember how Hook's law
Speaker 1: helps you more or less accurately weigh your fruit and
Speaker 1: vegetables on the spring scale at the grocery store. It
Speaker 1: also underlies the operation of one of the smallest force
Speaker 1: measuring devices in the world, the atomic force microscope, used
Speaker 1: in biochemistry, biology, and materials engineering. Such microscopes use a
Speaker 1: micron scale silicon or silicon nitride cantilever, which is a
Speaker 1: spring like beam supported only on one side to detect
Speaker 1: nano Neewton and peak Newton tugs forces on the scale
Speaker 1: of intermolecular attractions. Today's episode is based on the article
Speaker 1: how digital scales work on HowStuffWorks dot Com, written by
Speaker 1: Nicholas Jerbis. Brain Stuff is production of by Heart Radio
Speaker 1: in partnership with HowStuffWorks dot Com and is produced by
Speaker 1: Tyler Klang. For more podcasts from my heart Radio, visit
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