Because perfect and total accuracy is not possible to achieve with any scale technology, the goal of most industries is to achieve the highest level of accuracy possible while keeping costs in check. Accuracy is measured in terms of the error rate produced by the scale. The Full Scale (F.S.) accuracy rate is expressed as a percentage or ratio. For example, if precision scales are touted to have an error rate of 1 percent or less, the accuracy rate is expressed as 1%F.S. The resolution ratio expresses the error rate when compared to the weight load. For example, a resolution of 1:5,000 expresses the scales’ error rate of accuracy to within .01 lb. for a load of 50 lbs. The same ratio for a 100 lb. load will have an error rate of about .02 lb.
Strain Gauge Scales
Strain gauge scales measure the strain of the item being weighed. Examples of a strain gauge scales are the electronic bathroom scale and food scales, such as those that may be found at the deli or meat counter in supermarkets. In both cases, these scales combine spring technology with strain gauge technology to produce an acceptable level of accuracy for weighing food or people.
This type of scale operates on the principle of a small coil of wire mounted to a load cell. The load cell houses a spring element that acts as a sensor. When an object, or load, is placed on the weighing platform, the spring in the load cell bends or stretches. The attached thin wire follows the movement of the spring. When no load is applied to the load cell, the wire tracks the resistance and provides a baseline of weight. The scale is then calibrated to zero. When a load is placed on the load cell, the wire tracks the resistance of the spring and provides a weight measurement for the load. Strain gauge technology has evolved over the years. Accuracy has greatly improved, but this type of technology always presents errors in measurement and a lower level of accuracy than other precision weighing technologies.
Strain gauge scales are cost effective. However, they are the least accurate of the three technologies. In addition, strain gauge scales tend to drift in accuracy with temperature changes. Standard strain gauge technology is often used in scales for industrial applications that require a standard level of accuracy, such as measuring gravel. We produce strain gauge scales with standard accuracy and 2x, or double accuracy, scales for better performance when a higher level of accuracy is required. The error rate of our standard strain gauge scales is 1:5,000, and for double accuracy scales, the ratio is 1:10,000.
Strain gauge technology is still only able to produce a certain level of accuracy. In addition, strain gauge technology is susceptible to certain errors, such as those that occur due to temperature. These scales also generate errors when the load cell is fully loaded. Some vendors have applied compensation strategies to improve resolution ratios for their products. However, actual accuracy of the strain gauge technology remains fairly constant and little is gained from such compensation strategies. When a high level of accuracy is required, particularly for heavier loads, other weighing technologies provide more accurate readings than strain gauge technology.
Force Motor Scales
Force motor scales are also known as electromagnetic force restoration’ scales. Force motor scales utilize a technology that measures electromagnetic force opposing the weight of the load. Force motor scales are often used in analytical and laboratory applications. Accuracy ratios of 1:150,000 or more may be achieved with force motor scales.
These scales, however, also produce errors with temperature fluctuations and exhibit drift. Additionally, these scales are difficult to utilize for weight loads over 50 lbs. Force motor scales are easily damaged by over-loading and are highly susceptible to shock damage.
Force motor scales provide a higher level of accuracy than with other technologies, such as strain gauge technology. For lower capacity loads, such as for use in laboratories, force motor scales are a much better solution than strain gauge technology. However, this technology is prohibitively expensive for higher capacity loads.
Our Ultra Precision Surface Acoustic Wave (SAW) Scales
Arlyn Scales has patented a new Ultra Precision Surface Acoustic Wave, or SAW,’ scale that utilizes a technology similar to what is used to weigh semiconductor circuits during manufacturing. Arlyn Ultra Precision SAW scales provide an extremely high resolution rate, yet they are a cost effective solution for heavier loads. Our Ultra Precision SAW scales resolution rate is between 1:100,000 and 1:200,000. Ultra Precision SAW scales are equipped with a large, durable rigid load cell block which provides protection against shock and over-load damage.
Our Ultra Precision SAW scales are approximately 20 times more accurate than standard strain gauge scales. These Ultra Precision SAW scales exhibit a similar precision to scales that utilize force motor technology. However, our Ultra Precision SAW scales are much more cost effective for heavier loads. The most amazing feature of our Ultra Precision SAW scales is that they cost about the same as a higher-end strain gauge scale. Ultra Precision SAW scales are roughly one-third the cost of force restoration scales designed for heavier loads.
In addition, our Ultra Precision SAW scales are much more durable and rugged than either strain gauge or force motor models, with an overload capacity of up to 500 percent. Resolution ratios are comparable in all error readings to force motor scales, and exhibit much more precision than any strain gauge technology. Currently, our Ultra Precision SAW scales are available in capacities up to 500 lbs. Soon, these precision models will be available for loads up to 5,000 lbs.
To learn more about our Ultra Precision SAW scales check our online catalog. If you have any questions or looking for further information, please do not hesitate to contact us. It is our pleasure to help you.