As a New York based scales manufacturer, Arlyn Scales has better insight into the struggles many industries face when it comes to finding a precision scale at a price that works with their budget. We’ve been designing and fabricating our scales in our Long Island factory for over thirty years now as well as their subassemblies, which include load cells, microprocessor instrumentation, and computer software.
While we manufacture a wide variety of scales, including bench scales, platform and floor scales, cylinder and vet scales, and explosion proof scales among others, which feature more precise strain gage load cells, one of our most popular lines is our ultra precision scales, which uses our internationally patented surface acoustic wave, or SAW, technology.
To understand what makes our ultra precision scales so precise, it is first necessary to understand what a strain gage load cell is and why, even with our superior construction, it will not always provide the kind of precision a company may need.
Strain Gage Load Cells
A transducer is a device that converts a signal in one form of energy to another; a load cell is equipped with transducers that convert force into an electrical signal Ð in this case, strain gages. Strain gage load cells have been the most popular transducers in the weighing industry for the last sixty or so years, however, they’re not all created equally.
A load cell is a piece of metal within the scale that has one end attached to the underside of the scale’s platform and the other attached to the interior floor of the scale. Any weight placed on the platform is transferred to the load cell, which bends under the force of the load.
When we manufacture our load cells, they are precisely machined using computer controlled devices. During this process, we incorporate four thin sections into the load cell design, which are called flexures. The strain gage transducers are bonded to these flexures and wired together to form a Wheatstone’s bridge.
When a load is placed on the scale platform the load cell bends, which also causes the flexures to bend. When the flexures bend the resistance of the gages changes, which alters the voltage output of the bridge. The voltage is then translated into numeric form by an Analog to Digital converter and, because all these changes are proportional to one another, the output value seen on the scale’s indicator corresponds to the weight of the load on the platform.
To understand what kind of precision a strain gage load cell offers, let’s take a look at the Arlyn 320D and 320M Platform Scale models as an example.
The 320D has a capacity of 500 pounds and a resolution of one-tenth of a pound (0.1lb). This means the scale has the ability to display 5,000 different units ranging from 000.0 to 500.0 and you would say it has a readability of one part in five thousand.
The 320M has a capacity of 1,000 pounds and a resolution of two-tenths of a pound (0.2lb). So the capacity is double that of the 320D model, but the resolution is only half as good. A resolution of two-tenths of a pound means that the scale only displays even digits after the decimal place (0.2, 0.4, 0.6, 0.8, 0.0). Yet this scale also has a readability of one part in five thousand.
As you explore this phenomenon, you’ll realize that there is a direct relationship between the capacity and resolution of a strain gage scale. Ultimately, the higher the capacity of the scale, the lower its resolution. This is true because strain gages arenÕt able to stretch far enough to achieve an accurate, high resolution measurement. Compare it to a Slinky. It can only be bent and twisted so far or so much before it loses its ability to do what it was designed to do and becomes damaged when it’s forced to. The same is true for strain gages. Once damaged, the measurements they provide will be inaccurate.
All of our strain gage load cells are manufactured out of stainless steel, which is more durable and less subject to distortion than the aluminum load cells the majority of our competitors use. They are able to bend further and retain their shape, which add years of useful life to each scale we make.
Ultra Precision Scales with SAW Technology
For most businesses, a readability of one part in five thousand is more than enough to satisfy their needs. However, there are other industries that require a much finer resolution than any strain gage scale can provide. Think chemical companies, paint mixers, and pharmaceutical manufacturers.
While we use the same theory of load cell design in our ultra precision scales, we use completely different transducers Ð surface acoustic wave, or SAW, transducerss.
SAW load cells feature two transducers, one on either side of the spring element. One of these acts as a transmitter and the other a receiver. The receiver detects the surface acoustic wave coming from the transmitter. This wave is then amplified by an amplifier and sent back to the transmitter, where the process starts over. The frequency of the wave depends on the distance between the transducers, which is at a reference position when the scale is at rest. When weight is applied to the platform, the load cell bends and the distance increases, which increases the frequency of the wave. The frequency is measured digitally and the signal is sent directly to the indicator where the numeric value is displayed.
The design of our SAW load cells is inherently better than that of any strain gage load cells for a number of reasons.
A thicker piece of metal is used in the load cell, which isnÕt possible with the strain gage design, which makes these load cells automatically more robust. It also improves their performance because they are less subject to distortion from outside forces such as temperature changes, wind currents, shock loading, and overloading.
The frequency is measured digitally, which means there is no need for an analog to digital signal conversion, which makes these scales inherently more accurate. They also provide much finer resolutions and are more stable over time.
The largest benefit, however, is their ability to provide extremely accurate, precision resolution. To compare the incredible resolution of our ultra precision scales to our strain gage ones, letÕs use our 620X Strain Gage Bench Scale and our SAW-X and SAW-C Ultra Precision Scales as an example.
The 620X model has a ten pound capacity and a resolution of two thousandths of a pound (0.002lb). Our SAW-X model has the same ten pound capacity but has twenty times the resolution at one ten-thousandth of a pound (0.0001) and a readability of one part in 100,000.
The SAW scale is twenty times more accurate than the strain gage scale. Remember the general rule for determining the resolution of a strain gage scale? Divide the capacity by 5,000? Well, to determine the resolution of a SAW scale, you divide the capacity by 100,000.
LetÕs also compare the 620X to the SAW-C scale. At 100 pounds, the SAW-C model has ten times the capacity of the 620X. However, if you divide this by 100,000, youÕll see that the SAW-X has a resolution of one thousandth of a pound (0.001lb) and a readability of one in 100,000. This is double the accuracy of the ten pound strain gage scale at ten times the capacity!
Our ultra precision scales eradicate the capacity/resolution dichotomy that exists within strain gage scale design. Businesses can now choose both high capacity and high resolution. Unlike other precision scales, which cap out at around fifty pounds, we’re able to offer these fine resolutions with capacities up to 500 pounds, which has a resolution of five thousandths of a pound (0.005lb), unlike the 500 pound strain gage scale which has a resolution of (0.1lb).
And since we manufacture and distribute our scales from within the United States, we’re able to offer factory direct pricing, which means these unrivaled scales are available for a cost similar to that of a high-end strain gage scale. If you’ve ever shopped for a magnetic force restoration scale, you know exactly what kind of savings this can mean for your company.
Contact Arlyn Scales
If you’re still unsure which of our precision scales would meet your need or have any questions at all, contact us today. Our customer support staff will take the time to understand your unique situation and help guide you to the best, lowest cost option available to you.
Since we are an actual manufacturer and not just a distributor, we can also offer custom designs, so be sure to ask about your options if you’re not sure our standard models will fit where you need them most.
