That’s right! The strain gauge load cell.
Do you know what’s wrong with it?
No? Well, that could be because it meets your accuracy requirements and you’ve never really had to think about it.
But those companies that require extremely fine resolutions and precise measurements may at least be familiar with its limitations. These companies include paint mixers, professional and university laboratories, semiconductor manufacturers, those that handle expensive minerals, and others that must keep an inventory of extremely small, lightweight parts.
The Limitations of Strain Gage Scales
A strain gage load cells works by measuring the stress, sometimes called strain, placed on the spring element of the load cell. When a load is placed on the scale’s platform, this piece of metal bends in direct proportion with the weight of the load. To measure how far it bends, the spring element has strain gages attached to its flexors. These gages are wired together to form a Wheatstone’s bridge. So weight is applied to the platform, the spring element bends, the flexors bend, the strain gages change in resistance, and the voltage output of the bridge changes. This voltage is then passed through an Analog to Digital Converter and the digital signal is sent to the scale’s indicator where your read the weight as a set of numerical digits.
However, strain gages aren’t able to detect extremely slight changes in weight and generally offer a readability of 1 part in 5,000 pieces. Essentially, the readability of a scale is a measure of its performance. Determined by dividing a scale’s maximum capacity (for example, 100 lbs) by its resolution (or the number of decimal places to which the scale can accurately read, for example, 0.01 lb), it means that the scale can display 5,000 different weights (100 / 0.01 = 5,000). And while this may initially seem like a lot, it’s actually fairly small. So while it meets the needs of most businesses, it doesn’t account for the high resolution measurements these other companies require.
Other disadvantages include:
- Vulnerability to damage from shock loading (dropping a load onto the scale from a height) and overloading (putting a load on the scale that’s greater than its maximum capacity)
- The Analog to Digital Conversion that reduces the accuracy of the measurement
- Drops in accuracy due to changes in temperature
- Adhesives are used to place the spring element within the scale, which results in a loss of flexibility of the spring element load cell
- A relationship between the capacity and resolution where the resolution diminishes as the capacity increases
So What Is An Surface Acoustic Wave Sensor?
Available only from Arlyn Scales, surface acoustic wave SAW (Technology) is the solution to businesses that struggle to find affordable, high precision scales with a resolution that’s fine enough to meet their needs.
While our SAW load cells feature the similar basic theory of load cell design as our strain gage models and use a spring element to detect changes in weight, the similarities end there.
How Is It Different From Strain Gage Sensors?
Instead of measuring stress or strain, our ultra precision SAW scales measure displacement, which reduces strain levels to less than 10% of those found in strain gage scales. This makes them more reliable in and better suited to industrial environments because they have a higher overload capacity that makes them more resistant to damage from shock and overloading, which are two major causes of scale failure. So you don’t have to be extra careful using these scales, even though they’re amazingly accurate. Able to accept up to 2.5 times the rated load without damage, these scales were designed to be used in harsh industrial environments.
Measurements are also taken digitally, which makes these scales inherently more accurate and increases their sensitivity to smaller changes in weight. The spring element in a SAW load cell has two transducers attached to it. One acts as a transmitter and the other a receiver. The transmitter creates a bulk wave and passes it to the receiver where it is amplified and sent back to the transmitter, where the process repeats. When the spring element bends, the frequency of this wave changes. By digitally measuring this frequency, we’re able to determine the weight of the load placed on the platform.
SAW load cells also provide a higher resolution at higher capacities than their strain gage counterparts. Compared to 1 part in 5,000 for strain gage scales, our SAW load cells offer a readability of 1 part in 100,000, which is 20 times better.
So while a 50 pound capacity strain gage scale has a resolution of 0.01 lb, a SAW scale with the same capacity would offer a resolution of 0.0005 lb.
The chart below highlights the difference in the resolution these two technologies offer at the same maximum capacities:
|Resolution of a SAW Scale
|Resolution of Strain Gage
And while changes in temperature will cause changes in the weight reading of all scales, our SAW scales reduce this problem dramatically. Readings will change less than 3 parts per million for each change in temperature of 1¡C, which means better consistency.
Advantages of Our Factory Direct Operation
Arlyn Scales is an direct manufacturer and distributor of our products. Made in our New York factory, we ship our products to you directly from our location. This significantly reduces costs and we’re able to pass the savings on to you. It also allows us to invest in research, design and development of new scale technologies (such as SAW load cells), which means you’re getting a higher quality product at an extremely competitive price.
And since we do the manufacturing ourselves, we’re also able to provide you with custom solutions. Need a platform size not available on our site? No problem! Need a specific connection port? No problem! We can add Wi-Fi, Ethernet, USB, Cloud, RS-232, 4 Ð 20 ma or any other connection you need. Need your scale to automate certain processes within your production line? No problem! Ask about our setpoint controller.
Contact Arlyn Scales
If you’d like to learn more about our SAW scales, are interested in making a purchase or would like guidance in making a selection before you order online, contact us today! We’re here to help.