# Accuracy and Benefits of Industrial Counting Scales

Industrial counting scales are perfect for keeping an inventory of small pieces or parts because they can easily convert the weight of an entire batch into the number of individual pieces it contains.

Once the weight of a sample from the batch is calculated, the scale can weigh large batches of parts and determine the exact number of parts it contains, which makes inventory tracking fast and easy.

## The Accuracy of Sample Weight

Yet their usefulness depends on the accuracy of the sample weight. While the process seems pretty straightforward, not all counting scales will calculate piece weight properly.

Most inaccuracies are caused by errors during the sampling process. Arlyn scales use high precision measurements and advanced digital algorithms to ensure accuracy while maintaining speed and ease of use.

## Calculating Error in Sample Weight

Let’s imagine you’re using a standard industrial scale with a 100 lb. capacity and a 0.02 lb. resolution.

You have a sample size of 10 pieces and a sample weight of .0954 lb.

Using the 100 lb. capacity scale, the weight of a 10-piece batch would be 0.954 lb.

Yet your scale is only able to read to its best resolution, which means your scale would display 0.96 lb.

That’s a fairly significant error of 2.5%, which would affect the accuracy of all batches weighed based on this sample.

## Arlyn Ultra Precision Scales Reduce Error

With a SAW-C scale from Arlyn, you would have the same 100 lb. capacity but a much better resolution of 0.001 lb.

Using the same sample weight (0.0954 lb.) and sample size (10 pieces), the weight of the sample would be the same 0.954 lb.

Yet your scale would be reading to a much better resolution, which means it would read 0.954 lb.

This reduces the error to a negligible 0.03%, ensuring that your inventory totals are extremely precise.

## A New Precision Technology

The lower margin of error seen with the SAW-C scale is achieved thanks to a breakthrough weighing technology called surface acoustic wave. It’s the first new weighing technology to be introduced in the last 40 years and uses special weighing components to replace the strain gage system your standard scale most likely has.

## Understanding Strain Gage Weighing Systems

Within each scale is a type of resistor system called a load cell. Within the load cell is a specialized metal strip called a spring element that’s attached to the underside of the scale platform and the bottom of the scale floor.

When weight is applied to the platform it creates stress in the spring element, causing it to bend. How far the spring bends is directly proportional to the applied weight. You can think of it like a diving board, where an adult would cause the board to bend more than a child would.

During the manufacturing process, four thin sections called flexures are incorporated into the design of the spring element. Strain gage sensors are bonded to these flexures and wired together to form a Wheatstone’s bridge. The bridge is a type of electrical circuit used to measure an unknown electrical resistance.

So when you put something on a scale, this is actually what’s happening:

•    The spring element bends, causing the flexures to bend
•    The bending of the flexures changes the resistance of the strain gage sensors
•    The changing resistance of the strain gages alters the voltage output of the bridge
•    The voltage produced by the bridge is passed through an ADC (analog-to-digital signal converter)
•    The digital signal is sent to the scale’s display
•    You read the weight of the object you placed on the platform

## Why This Creates a High Margin of Error

The adhesive used to bond the strain gage to the spring element within the scale lacks the tensile quality seen in the spring element, which limits the element’s range of motion and therefore its ability to generate accurate, high resolution measurements. The ADC conversion also affects accuracy.

So while strain gage technology is well suited to general weighing tasks, it doesn’t have the high precision that’s a necessary part of weighing extremely lightweight objects like the ones in our earlier sample. This is why the margin of error is so high. It’s not that strain gage scales aren’t accurate—they’re actually perfect for the majority of weighing applications—it’s just not accurate enough for small parts counting.

## Comparison With Surface Acoustic Wave Technology

Instead of measuring the stress in the spring element, our Ultra Precision scales use surface acoustic wave technology (SAW) to measure displacement. This means measurements are inherently more accurate and higher resolution.

Our Ultra Precision scales still use the same basic theory of load cell design that calls for a spring element. However, we attach two SAW transducers to the element instead of strain gages. The substrate material of these transducers is a crystalline structure composed of lithium niobate. When weight is applied to the platform, the spring element bends. A bulk wave is created in the metalized pattern of the transmitting transducer that is sent through the substrate where it travels the length of the transducer and generates an equivalent signal on a second parallel substrate.

Another metalized pattern on the substrate of the second transducer acts as a receiver. The signal is fed back between these two transducers, creating a frequency between them. The rate of oscillation depends on the distance between the transducers, which is ultimately determined by the bending of the spring element.

The frequency of the wave is measured digitally, which makes the SAW scale inherently more precise and accurate than a strain gage scale that requires an analog to digital signal conversion.

While a strain gage scale has an average readability of 1 part in 5,000, our Ultra Precision scales have an incredible readability of 1 part in 100,000—a resolution that is 20 times higher than a strain gage scale at the same maximum capacity—which is why our counting scales have a significantly reduced margin of error.

## Perfecting the Sampling Process With Our Quick Count Feature

Our engineers have developed the Quick Count feature to ensure that every sample is taken accurately with no mistakes. With no confusing menu functions, you’re able to take a single sample weight for a specific piece and store it in the scale’s memory.

You don’t have to sample the parts every time you count inventory. You sample the product once and bypass that step in every future count. This ensures that every count will be consistent because they’ll all be based on the same accurately measured sample.

If you have a large inventory where the same parts must be stored in multiple containers, you can use our accumulation function to keep a running count and inventory one product in a single cycle.

## Inventory Data Is Meant to Be Shared

We offer a variety of I/O ports and connections to ensure that our Ultra Precision Counting Scale integrates flawlessly with your internal communication systems. These include WiFi, Ethernet, USB, flash drive, Cloud, RS-232 and more.

If you’d like to learn more about our precision counting scales or discuss the specs for a custom inventory system, contact Arlyn Scales today!