Over the course of time, people have always strived to achieve more accurate measurements. In the case of length and distance, original measurements were based on parts of the body, such as a hand or foot. These measurements became more accurate when standard rulers were introduced. A known, reproducible standard would 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 between the 2 marks was defined as a meter. This distance was designed to represent a fraction of one ten millionth of the distance from the equator to the North Pole. The bar material was made from platinum iridium, which is very stable. It was stored in an area where the environmental conditions, including temperature, were kept as constant as possible. Copies of this bar could be produced and sent to different locations. More recently, 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 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 sundials, which could divide a day into a number of parts. Special candles were built that were meant to burn at a steady rate, therefore providing more accuracy. 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 measurement 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. The product that needed to be weighed was placed on one end. Stones representing standard weights would be placed on the other pan until the rod was balanced. Some of the earliest known written histories dwell on the requirement for society to use true weights. An improvement was introduced with balances that used a pivot and a bearing. Then, a sliding weight was incorporated. Spring dial scales eliminated any requirement for weights. A more modern advancement was with the introduction of the strain gage. This device is a form of an electrical resistor. The value of the resistance would change as the strain gage was stretched. By attaching the gage to a specially shaped piece of metal, known as a load cell, the resistance would change proportionally to the bending of the load cell. A scale platform is attached to the load cell, so this change in resistance became proportional to the amount of weight on the scale platform. Most modern industrial scales are based on this principal. A single load cell may be used for a bench scale or parts counting scale. Four load cells mounted in the corners of the scale platform are used for drum scales, platform scales and floor scales. The accuracy of load cell scales can be quite good. A rule of thumb is that the combined errors due to temperature change, non linearity, drift, and a variety of others, will yield a total accuracy of 1/10 of 1%. Digital scales today regularly achieve that level. There are many applications that require much higher precision scales. These can occur in pharmaceutical, chemical, paint, and many other industries. Arlyn Scales has invented a technology, called Ultra Precision Surface Acoustic Wave Scales. These industrial scales include two semiconductor substrates. The frequency of oscillation of these devices is precisely proportional to the amount of weight on the electronic scale platform. The accuracy provided by these digital scales are twenty times more accurate than standard industrial scales. The total accuracy is better than 1/100 of 1%. For example, a 200 lb capacity ultra precision scale has a resolution of 0.001 lb. These high precision industrial scales are not very expensive. They have a cost that is similar to a high quality standard digital scale. This makes them ideal for formulation requirements, high precision parts counting, accurate filling, and flow rate monitoring.
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