When fractions of a pound can affect the quality of your final product, you need a high-resolution scale that provides superior performance. Whether you mix paint, manufacture semiconductors, run a laboratory or require decimal precision from your weighing instruments for any reason, chances are youÕre familiar with the difficult decision making process that comes with purchasing a new or replacement scale.
Issues with Strain Gage Models
These scales have been the industry standard for over sixty years now. And while appropriate for the majority of weighing applications, scales equipped with strain gage load cells simply arenÕt capable of providing the high-resolution measurements you need. This is especially true if you require a scale with a higher maximum capacity.
A load cell is a type of resistor. Essentially it is an aluminum or steel spring that is attached to the underside of the scale platform at one end and the base of the scale at the other. When weight is applied to the platform, the spring bends. Affixed to the flexures of this spring element are four strain gage transducers. When the spring element bends, the flexures bend and cause the resistance of the gages to change. This also changes the voltage of the WheatstoneÕs bridge the strain gage scales are wired to form. This voltage is passed through an analog-to-digital converter and sent to the digital display where the numeric measurement can be read.
However, the accuracy of these scales may not be the best possible for several reasons. The adhesive used to place the spring in the scale can have an adverse affect on the measurements taken. The spring has a tensile quality that the adhesive doesnÕt, which affects the flexibility of the spring and therefore its ability to generate an accurate reading.
The spring element must also be placed with extreme precision. A strain gage load cell is designed to detect vertical forces, but there are also horizontal forces that it must reject. ItÕs position within the scale affects how well it is able to manage these different forces.
As with most resistors, strain gages are also affected by changes in temperature that alter their resistance capacity. While technology has been created that attempts to compensate for this change, load cell output will still vary with temperature. Generally, a strain gage scale has an accuracy of about 0.1% and a resolution of 1 part in 5,000. If youÕre buying from a superior scale manufacturer, the resolution of a strain gage scale can reach 1 part in 10,000.
Ultimately, strain gages cannot bend far enough to provide a high resolution measurement without becoming deformed. And the higher the capacity of the scale, the lower its resolution. Those who require equipment for more sensitive measurements are not well served by these scales.
Force Restoration Scales: Too Sensitive?
While these scales meet the high-resolution requirement, they also pose issues of their own. Among these are extremely low maximum capacities and the need for an ideal weighing environment.
Force restoration scales utilize electromagnetic technology to support the weighing platform that must be directed by a precise flexure system. The electromagnetic current required to counteract the weight on the platform is directly proportional to the weight of the load. Weight is determined by the calculating the amount of current necessary to offset the load.
The flexure system that directs the platform is prone to damage due to side forces and shock loading, which means these scales are generally not well-suited to more industrial environments.
Because force restoration scales are sensitive to drifts in temperature, air currents, and vibrations from other equipment, theyÕre often housed in a plastic or Plexiglas enclosure, which can make them a hassle to use.
Another disadvantage is the inability of this design to weigh loads with larger capacities without mechanical support. And because the amount of current rises in proportion to the weight of the load, the current required for a large capacity load or large quantity of scales would become prohibitive.
Ultra Precision Technology from Arlyn Scales
Distinguished by their precise, high-resolution measurements and industrial-strength durability, these scales feature our internationally patented surface acoustic wave technology (SAW) and are the perfect solution for those who have struggled to find a scale that actually meets their weighing needs.
Instead of measuring the strain of the spring element, our ultra precision scales measure displacement using two SAW transducers, resulting in strain levels are less than 10% of those found in strain gage scales, which means readings are inherently more accurate.
We use a similar theory of load cell design in our ultra precision scales. Featuring a spring element, the substrate material of our SAW transducers is a crystalline structure composed of lithium niobate, through which a bulk wave runs. The wave is created by a metalized pattern that acts as a transmitter. The wave travels the length of the transducer and generates an equivalent signal on a second, parallel substrate.
A second metallized pattern on the second substrate acts as a receiver. The distance between the transmitter and receiver and the frequency of oscillation between them determines the displacement of the spring element, which is measured digitally.
While strain gage scales offer an accuracy of 0.1%, our ultra precision scales provide a much higher accuracy of .01% – the equivalent of force restoration scales. However, because the strain levels of the load cell are extremely low, these scales are 5 times more rugged than strain gage scales. TheyÕre as much as ten to twenty times more rugged than force restoration scales, being less sensitive to air currents and changes in temperature.
The lowest capacity available in our ultra precision line is 10 pounds, which provides accurate measurements up to .0001 pounds. The highest capacity is 500 pounds, which features an astonishing level of accuracy up to .005 pounds.
Our Ultra Precision Scales are as accurate as a force restoration scale but far more rugged, which makes the perfect for use in industrial environments that require sensitive, high-resolution measurements. TheyÕre also about one third the cost.
Arlyn Scales Weighing Solutions
Because weÕre a factory-direct scale manufacturer, you can rely on us to help guide you to the scale that best meets your needs. If we donÕt have anything in our inventory that does this, we can work with you to come up with a custom solution that will. While our scales are feature rich, you only pay for the ones you need. So contact us today to learn more about our ultra precision scales and all the ways you can use them!