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. However, over the entire course of history, scales have been just as important to the economy as they are today. The most ancient scales were simple balances. These devices consisted of a lever with two pans suspended at equal distances from the fulcrum. When an item (such as a sack of gold coins) was to be weighed, it would be placed in one of the pans. Known weights would then be added to and taken away from the pan on the other side of the fulcrum until the lever was perfectly balanced in a horizontal position. This indicated that the weight on one side of the lever was equal to the weight on the other side of the lever.
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. However, as opposed to the original simple balances, 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. Therefore, rather than requiring equivalent weights on both sides of the lever to put the balance and 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 other side of the lever. A third type of analog scale that has been developed is the spring scale. This scale relies on the concept that a force placed on a spring will stretch the spring a known distance if the spring constant of the spring 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, and where the force of the spring and the force of the object being weighed are in equilibrium, the correct weight can be read. One of the most well-known usage for spring scales 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. Today, analog scales are a perfect solution when a weight measurement does not have to be very precise. They are useful to determine a person’s body weight to within 1 pound, or to measure out a serving of meat to within a few ounces. However, they are not accurate enough for many industrial processes that require very high levels of precision. While a spring scale may have a resolution of 1 part per 100, industrial processes require resolutions of 1 part per 5000 or even higher. Digital scales have taken over as the most precise measuring devices and are by far the most widely used in industry. The electronic scales that are used in industry include bench scales, platform scales, floor scales, drum scales, 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 are resistors made up of folds of flat metal. When the load cell bends and the strain gauges are stretched, their resistance changes proportional to the amount of force acting on the load cell. The output signal from the strain gauges is sent to an analog to digital converter which outputs a final weight reading. Ordinary strain gauge digital scales have resolutions of about 1 part in 5,000. However, a new technology called Surface Acoustic Wave (SAW) technology has been developed by Arlyn Scales and incorporated into Arlyn’s Utra-Precision Industrial Scale Line. SAW scales have a resolution of an incredible 1 part in 100,000. These scales are particularly useful in situations where high precision is necessary, such as check weighing and polymer production.