The History of Scales
The History of Scales
If you were to travel back in time and show an ancient street merchant a digital weighing scale, he would have no idea what to do with it. Yet over the entire course of history, scales have been just as important to the economy as they are today, which is why people have always strived—and continue to strive—for more accurate measurements.
Before standardized equipment, many measurements were based on parts of the body, such as a hand or foot—hence the American “feet.” These measurements became more accurate when standard rulers were introduced. A known, reproducible standard would then serve a specific geographic area.
Later, agreements were made to produce a standard metal bar with two marks that was very carefully produced. The distance was designed to represent a fraction of one ten-millionth of the distance from the equator to the north pole.
The bar was made from a very stable material called platinum iridium and was stored in an area where environmental conditions like temperature were kept as constant as possible. Copies of this bar could be reproduced and sent to different locations.
More recently, however, the definition of a meter was changed to be even more accurate. It was defined as the distance that light would travel in a particular, very small fraction of a second. This distance is very standard and can be reproduced anywhere.
Similarly, the measurement of time has also become much more accurate over the course of history. The earliest measurements were based on the length of a day, or the amount of time between sunrise and sunset.
More accuracy was obtained with the invention of the sundial, which could divide a day into a number of parts. Special candles were built that were meant to burn at a steady rate, which provided a more accurate means of telling time.
Hourglasses, water clocks and then pendulum clocks provided significant improvements. Much more recent clocks utilized electronic devices such as a tuning fork, a quartz crystal and then atomic clocks for vast improvements.
Weight measurements and scales have followed a very similar path. Some of the earliest examples of weight measurement were a simple rod that was suspended by a string in the middle. A pan was attached to each end and the product that needed to be placed in one pan, while stones representing a known weight were added to the other until the rod was balanced.
In fact, many of our earliest known written histories dwell on the requirement for society to use “true weights.”
The most ancient scales were rudimentary balances consisting of a lever with two pans suspended at equal distances from the fulcrum. When an item—such as a sack of gold coins—needed to be weighed, it would be placed in one of the pans. Known weights would then be added to and taken away from the opposite pan until the lever was perfectly balanced in a horizontal position. By calculating the total of the known weights, it was possible to determine the weight of the object in the other pan.
This system and similar variations were used until the late 1700s when new weighing technologies were invented. However, these inventions were not as accurate as the electronic systems that were designed and perfected in the 20thand 21st centuries.
The Triple-Beam Balance
More recently, the much more practical and intricate triple-beam balance was created. This device also uses a lever system in which the force on one side of the fulcrum is balanced with the force on the other side of the fulcrum.
Unlike the original simple balance, however, the triple-beam balance takes advantage of the concept that a mass further away from the fulcrum of the lever creates more force on the lever than a mass that is closer to the lever.
So rather than requiring equivalent weights on both sides of the lever to put the balance in equilibrium, the triple-beam balance is used by moving smaller weights closer and further from the fulcrum to balance out the weight of the object on the opposite side of the lever.
It’s likely that you’ve used this type of scale in your middle or high school physical science class.
The next innovation was an analog scale called a spring scale, which relies on the concept that a force placed on a spring will stretch the spring a known distance its “spring constant” is known.
An indicator on the spring will move up and down a set distance against a gauge, which is marked with various weight measurements. When the force of the spring and the force of the object being weighed are in equilibrium, the correct weight can be read.
The most common type of spring scale is the bathroom scale, which combines the force of four levers coming from each corner of the scale to stretch a spring and spin a gauge.
Analog Scales in Today’s World
Analog scales are a perfect solution when a weight measurement doesn’t have to be very precise. They can determine a person’s body weight to within a pound or measure a serving of meat to within a few ounces.
However, they aren’t accurate enough for many industrial processes that require a higher level of precision. While a spring scale may have a resolution of 1 part in 100, industrial processes commonly require resolutions of 1 part in 5,000 or higher.
Since their inception, digital scales have taken over as the most precise measuring devices and are by far the mostly widely used in industry. These electronic scales include bench, platform, floor, drum and cylinder scales.
The weight transducer used in digital industrial scales is called a strain gauge load cell. The load cell is a block of metal that is shaped in a way so that it bends, much like a spring, in a very predictable manner when a force acts upon it. Additionally, like a spring, when the force is removed, the load cell moves back to its original configuration.
Attached to the load cell are several strain gauges. These resistors are made up of folds of flat metal. When the load cell bends and the strain gages are stretched, their resistance changes proportional to the amount of force acting on the load cell. The output signal from the strain gages is sent to an ADC (analog-to-digital converter), which outputs a final weight reading.
Ultra Precision Scales
Ordinary strain gauge digital scales have resolutions of about 1 part in 5,000 and an accuracy of about 1/10 of 1%. However, this still isn’t as precise as some industries require, which is why we’ve developed a new weighing technology called Surface Acoustic Wave (SAW) and designed a new line of Ultra Precision industrial scales.
These industrial scales use two semiconductor substrates and SAW transducers. When weight is applied to the scale, it creates a bulk wave that travels between the transducers. The frequency of oscillation of these devices is directly proportional to the weight on the scale platform. By measuring this digitally, we’re able to offer resolutions of 1 part in 100,000 and accuracy of 1/100 of 1%.
These scales are particularly useful in situations where high precision is necessary, such as check weighing, small parts counting, accurate filling, flow rate monitoring and polymer production. The pharmaceutical, chemical, paint and many other industries rely on this Ultra Precision technology.
Arlyn Scales’ history is one of advancement and innovation, and so is our future. We’re currently working on several projects that will allow us to upgrade the accuracy of our scales even further, improve the interface of our digital indicators and advance system communication through our SAW technology, Android interfaces and Cloud computing systems.
To learn more about the innovations happening at Arlyn Scales or to discuss your unique weighing needs, contact us today!