The High Precision of Industrial Bench Scales

The High Precision of Industrial Bench ScalesBench scales are commonly used in food, chemical, shipping and receiving, medical, pharmaceutical and retail industries. They’re also commonly used for small parts counting.

When a company is in the market for a new bench scale, they have two predominant weighing technologies to choose from — strain gage and force motor.

The decision will ultimately rest on the level of accuracy required in the company’s daily tasks and the cost of the scale.

Strain gage scales provide good accuracy at lower costs while force motor scales provide excellent accuracy at much higher costs.

Arlyn Scales has introduced a third new weighing technology that rivals the accuracy of force motor scales at a cost more similar to quality strain gage scales.

Useful Definitions

•    Resolution: The smallest increment of weight that the scale’s numeric display can indicate. Usually written as a decimal, e.g., 0.2 lb.

•    Readability: The smallest division at which the scale’s display increments. Essentially the same as resolution, but usually written as parts of a whole or as a ratio, e.g., 1 part in 5,000 or 1 : 5,000.

•    Accuracy: The extent to which the value displayed by the scale equals the true value of an object’s weight. Usually expressed as a fraction of a percentage, e.g., 1/10 of 1% or as a range, e.g., ±0.1 lb.

Standard Strain Gage Bench Scales

The most widespread weighing technology, it’s also the least expensive. These scales use strain gage resistors to determine the amount of stress / strain placed on a spring element when weight is applied to the scale platform.

The average strain gage bench scale has a readability of 1 part in 5,000. This means the scale can display 5,000 unique weight measurements.

To determine the resolution of the scale, you simply divide the readability and multiply the result by the scale’s capacity. For example:

•    A bench scale with a 10 lb. capacity would have a resolution of 0.002 lb.
o    (1 / 5000) * 10 = 0.002

•    A bench scale with a 50 lb. capacity would have a resolution of 0.01 lb.
o    (1 / 5000) * 50 = 0.01

•    Likewise, a scale with a 100 lb. capacity would have a resolution of 0.02 lb.
o    (1 / 5000) * 100 = 0.02

Advanced Strain Gage Technology

The readability of the highest quality strain gage scale is no higher than 1 : 10,000. This means that the same capacity scales would offer double the accuracy of the average strain gage scale.

•    10 lb. capacity = 0.001 lb. resolution
•    50 lb. capacity = 0.005 lb. resolution
•    100 lb. capacity = 0.01 lb. resolution

These scales are typically accurate to 1/10 of 1%. This means the true value of the object’s weight will be within ±0.1 lb. of the displayed weight.

So while the 50 lb. capacity scale can read to five thousandths of a pound, the measurement is reliably accurate to only a tenth of a pound.

This level of accuracy is appropriate for weighing tasks that don’t require pinpoint accuracy such as food manufacture or shipping. Even the advanced strain gage scale would not be useful in ink and dye manufacture or small parts counting.

Good Accuracy Is Not Always Good Enough

That’s why force motor scales were invented. Based on a completely different weighing technology, they offer a much higher readability of 1 : 150,000 and offer excellent accuracy for paint mixing and other high-precision tasks.

However, there are some issues with force motor scales that make it less than ideal for industrial use.

In this design, an electromagnet is used to support the scale platform. The electrical current required to balance the platform when weight is applied varies based on the weight. Weight is determined by measuring the current.

While this is an intrinsically accurate method for determining weight, it’s also very costly, prone to error and prohibitive at higher capacities. Changes in temperature, air currents and vibration caused by other equipment can all affect these scales’ accuracy.

Their accuracy characteristics also change over time, which can introduce error. This means the scale must be manufactured with an internal calibration device applied to the sensor. Recalibration must be performed often to maintain accurate results.

While this is a sensible solution at smaller capacities, which cap around 50 lbs., it becomes impractical at higher ones because more electrical current and increasingly expensive and complex systems are required to counteract the weight and maintain accuracy.

Arlyn Ultra Precision Scales

Instead of measuring stress and strain of a spring element like a strain gage scale, or measuring electrical current like a force motor scale, our Ultra Precision Scales measure the time it takes a bulk wave to travel from a transmitter to a receiver placed on the scale’s spring element.

This is a revolutionary idea because it allows us to digitally measure a precise weight using a spring element load cell, which is cheaper to manufacture, without any of the disadvantages seen when resistors are used.

The readability is equal to that of a force motor scale at 1 : 150,000 while maintaining an accuracy of 1/100 of 1% (±0.01 lb.), which is ten times better than strain gage.

•    A 10 lb. capacity SAW scale has a resolution of 0.0001 lb.
•    A 50 lb. capacity SAW scale has a resolution of 0.0005 lb.
•    A 100 lb. capacity SAW scale has a resolution of 0.001 lb.

That’s the same resolution for a 100 lb  capacity as the 10 lb. capacity advanced strain gage scale but with 10 times the capacity!

And while the readability is equal to or better than force motor, our Ultra Precision Scales are a third of the price.

USA Factory Direct

All Arlyn scales and weighing devices are manufactured right here in the US. We ship directly from our Long Island, NY factory, which means faster shipping at much lower costs. And since there are no middlemen to drive up prices simply for handling the product you pay only for the scale you need, which means you get extremely competitive pricing on higher quality products.

Order an Arlyn Ultra Precision Scale now or contact us with any questions you may have.