1 00:00:01,840 --> 00:00:07,600 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff, 2 00:00:07,640 --> 00:00:12,840 Speaker 1: Lauren Bogelbaum. Here, there's something so commonplace about a weighing 3 00:00:12,920 --> 00:00:17,639 Speaker 1: device that it's easy to forget its deeper significance, as 4 00:00:17,680 --> 00:00:20,760 Speaker 1: these slightly skewed spring scale in any local produce aisle 5 00:00:20,800 --> 00:00:24,239 Speaker 1: reminds us. The scale has long served humans as the 6 00:00:24,360 --> 00:00:28,000 Speaker 1: chief arbiter of commerce, the maker or breaker of shipping 7 00:00:28,000 --> 00:00:31,680 Speaker 1: budgets and carry on capacity, and the utility player of 8 00:00:31,760 --> 00:00:37,040 Speaker 1: the pharmaceutical bench. From the smallest, most fine tuned laboratory 9 00:00:37,080 --> 00:00:40,280 Speaker 1: balance to the pit and girder monsters that weigh train 10 00:00:40,400 --> 00:00:46,280 Speaker 1: cars and tractor trailers, scales make modern life possible. Scales, 11 00:00:46,560 --> 00:00:50,040 Speaker 1: or more specifically, balances weighed heavily on the minds of 12 00:00:50,120 --> 00:00:55,800 Speaker 1: ancient builders, inventors, and economic advisors. Too. Small balance weights 13 00:00:55,880 --> 00:00:58,600 Speaker 1: dating back to around five to six thousand years ago 14 00:00:58,680 --> 00:01:01,960 Speaker 1: provide some of the first hints of mankind evolving grasp 15 00:01:02,040 --> 00:01:06,480 Speaker 1: of science and mathematics. The most basic surviving balance from 16 00:01:06,560 --> 00:01:10,880 Speaker 1: Egypt predates the Dynastic period, placing its construction at earlier 17 00:01:10,880 --> 00:01:15,880 Speaker 1: than three thousand BCE. Like us, the ancient Egyptians applied 18 00:01:15,920 --> 00:01:19,000 Speaker 1: scales both in trade and in a saying ores and 19 00:01:19,080 --> 00:01:23,760 Speaker 1: alloys balances way an object by matching it against one 20 00:01:23,880 --> 00:01:27,280 Speaker 1: or more reference weights. They have a delicate touch and 21 00:01:27,400 --> 00:01:32,160 Speaker 1: are still used in laboratories. Scales use somewhat different physical 22 00:01:32,200 --> 00:01:35,800 Speaker 1: principles and mechanical components to measure weight in other forces. 23 00:01:37,040 --> 00:01:41,120 Speaker 1: Spring scales, for example, measure weight using Hook's law, by 24 00:01:41,120 --> 00:01:43,800 Speaker 1: which you can relate in objects weight to the stretching 25 00:01:44,080 --> 00:01:47,120 Speaker 1: or compression of a spring made from a given material. 26 00:01:48,400 --> 00:01:51,800 Speaker 1: Not all scales use springs, but all do measure weight 27 00:01:51,960 --> 00:01:57,800 Speaker 1: using mechanical components, So mechanical and digital scales differ only 28 00:01:57,880 --> 00:02:01,680 Speaker 1: in how they display that weight, mechanically like with a 29 00:02:01,720 --> 00:02:05,320 Speaker 1: needle on a dial, for example, or electronically alike with 30 00:02:05,440 --> 00:02:09,520 Speaker 1: an LED display. In a latter case, the scale employs 31 00:02:09,560 --> 00:02:13,440 Speaker 1: an analog to digital converter that translates the continuous readout 32 00:02:13,520 --> 00:02:17,600 Speaker 1: data from the scale into discrete digital information, much in 33 00:02:17,639 --> 00:02:20,760 Speaker 1: the same way that an MP three encoding scheme digitizes 34 00:02:20,840 --> 00:02:25,600 Speaker 1: the waveforms of music. An internal CPU converts the data 35 00:02:25,680 --> 00:02:28,880 Speaker 1: into input for a display board, which then shows the 36 00:02:28,919 --> 00:02:34,040 Speaker 1: result on a digital screen. Generally speaking, digital scales require 37 00:02:34,120 --> 00:02:37,799 Speaker 1: less expertise to use than those with mechanical readouts and 38 00:02:37,960 --> 00:02:42,480 Speaker 1: are capable of higher precision and faster processing. Still, the 39 00:02:42,520 --> 00:02:46,720 Speaker 1: capabilities of specific devices vary, particularly when the weights are 40 00:02:46,760 --> 00:02:51,519 Speaker 1: measured in tons. But let's talk more about those different 41 00:02:51,560 --> 00:02:56,239 Speaker 1: mechanical components that let us measure weight with scales. Think 42 00:02:56,280 --> 00:02:59,240 Speaker 1: of how a roadside carjack might lift a car via 43 00:02:59,360 --> 00:03:03,720 Speaker 1: mechanical adage the leverage of a handle or the inclined 44 00:03:03,760 --> 00:03:07,079 Speaker 1: plane of a screw, or how a car mechanic's hoist 45 00:03:07,160 --> 00:03:11,080 Speaker 1: might use hydraulic pressure in the same way. Different types 46 00:03:11,120 --> 00:03:14,799 Speaker 1: of scales weigh objects using a variety of operational principles, 47 00:03:15,040 --> 00:03:21,240 Speaker 1: like hydraulics, pneumatics, or bending beans. Scales come in all shapes, sizes, 48 00:03:21,280 --> 00:03:25,200 Speaker 1: and configurations, but the basic component doing the measuring is 49 00:03:25,320 --> 00:03:29,360 Speaker 1: nearly always a load cell. A load cell is a 50 00:03:29,480 --> 00:03:32,360 Speaker 1: kind of transducer, which is a term for a device 51 00:03:32,400 --> 00:03:36,880 Speaker 1: that converts one form of energy into another. Through load cells, 52 00:03:37,000 --> 00:03:41,240 Speaker 1: digital scales change mechanical energy the smooshing caused by a 53 00:03:41,320 --> 00:03:44,680 Speaker 1: sitting load or the stretching caused by a hanging load, 54 00:03:45,120 --> 00:03:50,880 Speaker 1: into an electrical effect. The widely used strain gage, for example, 55 00:03:51,200 --> 00:03:55,640 Speaker 1: reads compression or tension as tiny changes in electrical resistance 56 00:03:55,880 --> 00:04:00,480 Speaker 1: in what's called a whitstone bridge. Let's break that down 57 00:04:00,640 --> 00:04:06,080 Speaker 1: using a compression strain gauge as an example. Okay, Compression 58 00:04:06,080 --> 00:04:09,720 Speaker 1: occurs when an applied force reduces an object's volume, but 59 00:04:09,880 --> 00:04:12,760 Speaker 1: it can also refer to a more general decrease in 60 00:04:12,880 --> 00:04:18,120 Speaker 1: size along one or more dimensions. As it happens, squishing, 61 00:04:18,160 --> 00:04:23,960 Speaker 1: an electrically conductive material changes its electrical resistance because longer 62 00:04:24,000 --> 00:04:28,159 Speaker 1: and narrower wires are more electrically resistant than shorter and 63 00:04:28,240 --> 00:04:32,440 Speaker 1: wider wires. Think of it like water pumping through a pipe. 64 00:04:32,880 --> 00:04:35,719 Speaker 1: The longer and narrower the pipe, the harder it will 65 00:04:35,720 --> 00:04:40,839 Speaker 1: be to force water through it. Now, different materials experience 66 00:04:40,880 --> 00:04:44,760 Speaker 1: different changes in resistance during compression, a quality known as 67 00:04:44,839 --> 00:04:48,680 Speaker 1: gauge factor. A gauge factor can also alter in response 68 00:04:48,720 --> 00:04:53,000 Speaker 1: to temperature. The go to material for strain measurements is 69 00:04:53,040 --> 00:04:56,839 Speaker 1: called constantine alloy. It's usually fifty five percent copper and 70 00:04:56,920 --> 00:04:59,640 Speaker 1: forty five percent nickel, and it performs well at the 71 00:04:59,680 --> 00:05:03,840 Speaker 1: range temperatures that humans are comfortable at. To detect the 72 00:05:03,960 --> 00:05:07,560 Speaker 1: change in resistance caused by weight compression, one or more 73 00:05:07,600 --> 00:05:11,279 Speaker 1: strain gages are placed within what's called a whitstone bridge. 74 00:05:12,240 --> 00:05:15,159 Speaker 1: A whitstone bridge is an electrical circuit that can detect 75 00:05:15,200 --> 00:05:19,560 Speaker 1: an unknown electrical resistance by balancing it against known resistances 76 00:05:19,640 --> 00:05:23,200 Speaker 1: elsewhere in the circuit. In a sense, it's like a 77 00:05:23,240 --> 00:05:27,880 Speaker 1: balance scale for electrical resistance. The weight of the resistance 78 00:05:27,920 --> 00:05:30,880 Speaker 1: on one side tells you the unknown weight of the 79 00:05:30,960 --> 00:05:35,120 Speaker 1: resistance on the other. Strain gauges are the most widely 80 00:05:35,240 --> 00:05:38,760 Speaker 1: used type of load cell, but they're not the only one. 81 00:05:38,920 --> 00:05:42,800 Speaker 1: After all, research, industry, and commerce require the capacity to 82 00:05:42,839 --> 00:05:47,040 Speaker 1: measure weights under a seemingly limitless variety of environmental conditions 83 00:05:47,040 --> 00:05:52,480 Speaker 1: and space constraints, while also controlling for possible errors. Industries 84 00:05:52,520 --> 00:05:56,479 Speaker 1: that require greater safety and sterility often turn into pneumatic 85 00:05:56,520 --> 00:05:59,400 Speaker 1: load cells, which derive the weight of an object by 86 00:05:59,400 --> 00:06:04,360 Speaker 1: measuring the air pressure necessary to balance it. These blowhards 87 00:06:04,440 --> 00:06:07,520 Speaker 1: work well in the food industry and at hazardous sites 88 00:06:07,880 --> 00:06:11,000 Speaker 1: because they don't contain fluids that might seep, drip, or 89 00:06:11,120 --> 00:06:15,359 Speaker 1: spurt into the environment. Pneumatic cells can have a wide 90 00:06:15,440 --> 00:06:18,960 Speaker 1: range of weights with high accuracy, but they require a clean, 91 00:06:19,160 --> 00:06:22,640 Speaker 1: dry atmosphere and tend to take their sweet time responding 92 00:06:23,960 --> 00:06:26,840 Speaker 1: Hydraulic load cells, which measure load as a change in 93 00:06:26,880 --> 00:06:31,159 Speaker 1: fluid pressure are commonly found weighing tanks, bins, and hoppers. 94 00:06:32,360 --> 00:06:36,040 Speaker 1: Because they function without electricity, Hydraulic cells work well in 95 00:06:36,080 --> 00:06:39,520 Speaker 1: out of the way locals where power is a ify prospect. 96 00:06:40,800 --> 00:06:44,920 Speaker 1: They're pricey and complicated, but rugged they can handle million 97 00:06:44,960 --> 00:06:49,320 Speaker 1: pound loads. Load cells also come in all kinds of 98 00:06:49,320 --> 00:06:53,800 Speaker 1: different sizes, shapes, configurations, and materials, so that you can 99 00:06:53,920 --> 00:06:57,839 Speaker 1: use scales in different environments for different jobs. If you 100 00:06:57,880 --> 00:07:00,479 Speaker 1: need to take measurements in a wet environment, you can 101 00:07:00,560 --> 00:07:04,479 Speaker 1: opt for a hermetically sealed canister cell. If you're in 102 00:07:04,480 --> 00:07:07,640 Speaker 1: a facility concerned with height clearance issues, you can use 103 00:07:07,680 --> 00:07:11,560 Speaker 1: a thinner bending beam cell. And if you're expecting to 104 00:07:11,560 --> 00:07:15,440 Speaker 1: deal with extraneous forces affecting the load cell, say you're 105 00:07:15,560 --> 00:07:18,720 Speaker 1: using scales in a moving vehicle, in deep water or 106 00:07:18,760 --> 00:07:22,120 Speaker 1: on an aircraft, an s beam load cell that uses 107 00:07:22,120 --> 00:07:26,600 Speaker 1: a zigzag design can help control for that. Measuring force 108 00:07:26,720 --> 00:07:29,880 Speaker 1: is as fraught with technical troubles as any precision measurement, 109 00:07:30,320 --> 00:07:33,600 Speaker 1: which is no minor matter when one considers that piles 110 00:07:33,600 --> 00:07:37,320 Speaker 1: of money, and more importantly, human lives can rest on 111 00:07:37,360 --> 00:07:41,560 Speaker 1: the difference of a few grams. Researchers develop all kinds 112 00:07:41,600 --> 00:07:45,840 Speaker 1: of technologies to help make scales dependable in real world circumstances. 113 00:07:46,120 --> 00:07:51,080 Speaker 1: No matter the well scale, these devices could range from 114 00:07:51,120 --> 00:07:56,080 Speaker 1: being accurate in laboratory settings to highway weight enforcement and beyond. 115 00:07:56,880 --> 00:08:00,560 Speaker 1: On the larger end, scales employ levers to convert extra 116 00:08:00,640 --> 00:08:05,440 Speaker 1: large forces into manageable ones. Thus, the load cells in 117 00:08:05,480 --> 00:08:08,200 Speaker 1: some large truck scales only need to be able to 118 00:08:08,200 --> 00:08:11,320 Speaker 1: measure a fraction of the total weight, and thus can 119 00:08:11,400 --> 00:08:14,600 Speaker 1: easily handle between fifty to one hundred thousand pounds, which 120 00:08:14,640 --> 00:08:17,680 Speaker 1: is around twenty five to forty five thousand kilos, which 121 00:08:17,720 --> 00:08:21,800 Speaker 1: is a lot either way. And remember how Hook's law 122 00:08:21,880 --> 00:08:24,600 Speaker 1: helps you more or less accurately weigh your fruit and 123 00:08:24,680 --> 00:08:27,800 Speaker 1: vegetables on the spring scale at the grocery store. It 124 00:08:27,920 --> 00:08:30,920 Speaker 1: also underlies the operation of one of the smallest force 125 00:08:31,000 --> 00:08:35,199 Speaker 1: measuring devices in the world, the atomic force microscope, used 126 00:08:35,240 --> 00:08:40,960 Speaker 1: in biochemistry, biology, and materials engineering. Such microscopes use a 127 00:08:41,040 --> 00:08:46,080 Speaker 1: micron scale silicon or silicon nitride cantilever, which is a 128 00:08:46,240 --> 00:08:49,840 Speaker 1: spring like beam supported only on one side to detect 129 00:08:50,000 --> 00:08:53,960 Speaker 1: nano Neewton and peak Newton tugs forces on the scale 130 00:08:54,120 --> 00:09:02,880 Speaker 1: of intermolecular attractions. Today's episode is based on the article 131 00:09:03,040 --> 00:09:06,000 Speaker 1: how digital scales work on HowStuffWorks dot Com, written by 132 00:09:06,080 --> 00:09:09,160 Speaker 1: Nicholas Jerbis. Brain Stuff is production of by Heart Radio 133 00:09:09,280 --> 00:09:11,840 Speaker 1: in partnership with HowStuffWorks dot Com and is produced by 134 00:09:11,840 --> 00:09:15,320 Speaker 1: Tyler Klang. For more podcasts from my heart Radio, visit 135 00:09:15,360 --> 00:09:18,600 Speaker 1: the iHeartRadio app, Apple Podcasts, or wherever you listen to 136 00:09:18,640 --> 00:09:19,600 Speaker 1: your favorite shows.