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The Five Critical Factors of Load Cell Quality

Accurate data and high-quality test and measurement programs have many contributing factors. None are more important than the devices and equipment used on the test line. At Interface, we understand this better than anyone else.

Quality is why our force measurement products are used and known across multiple, highly regulated, and complex industries for providing the most reliable and accurate data anywhere. It is also why Interface is recognized as the preeminent leader in load cell quality.

How do we reach this high standard that we continue to hit with every product that leaves our facility? It is our overriding commitment to quality and consistency. The most important aspect of this is the fact that Interface controls the entire manufacturing process of our load cells. Many providers outsource certain components like that strain gages. We build the strain gages, the load cells, integrate the strain gages into the load cells and we do our own test, calibration, and quality inspection on each device.

Through our development process, which has been created and perfected over 52 years, we have learned what makes a great load cell. To start, Interface Chief Engineer Ken Vining outlines the top factors in load cell quality.

Five Most Critical Factors of Load Cell Quality

#1 Repeatability

Repeatability is first on the list and it is what our customers consider the most important aspect of buying an Interface load cell. Anyone can develop a load cell that is accurate for the first 10 to 15 measurements, but as environmental factors and stress are inflicted upon the load cell it needs to last. Due to our experience in this industry, we understand how certain temperatures, loads and other factors can diminish the accuracy of a load cell. This is one of the reasons we work so closely with our customers. Every application is different, and if we understand the application, we can deliver a custom load cell that withstands the various stressors over time without providing diminishing returns. This ensures that our customers receive the same, high-quality data after 10 years of use that they received on day one.

#2 Longevity

Like repeatable data accuracy over time, the load cell also needs to feature a high-quality and ruggedized build to last physically. Constant application of weight, pressure or torque can diminish the build quality and strength of a load cell if it does not meet the material requirements of the application. This can also reduce accuracy and lead to higher costs if customers must replace their load cells regularly. Interface has worked across a wide variety of industries and we understand the materials necessary for nearly any environment. With proper use, build quality and routine maintenance, load cells should last a very long time. In fact, Interface still has load cells in use in the field from when we started building quality product more than five decades ago.

#3 Accuracy

Data accuracy is affected by a litany of factors in load cells. In fact, we wrote an entire white paper on this very topic called, “Contributing Factors to Load Cell Accuracy.” Once again, the application of the load cell is what determines the conditions that affect accuracy. These conditions include creep, side and eccentric load, temperature, humidity, the mounting process and more. Interface can customize each of our load cells to ensure these conditions are accounted for to maintain premium accuracy.

#4 Sensitivity to Off-Axis Loads

A typical load cell is designed to measure load in one direction. However, nearly any project using force measurement test processes is going to introduce an off-axis load. If the load cell is not designed to adjust for this and compensate for what is called moment, the data output will be skewed. This is another reason that customers need to be extremely specific when discussing the application of the load cell. There are several ways to compensate for moment; however, most of these adjustments are physical and occur in the design and manufacturing process. With a correctly calibrated and designed load cell, off-axis loads will be eliminated and will not affect the accuracy of the data.

Special Note: Our recent release of the new ConvexBT product, the first to market miniature load button load cell that is designed to solve for off-axis (eccentric) loading. Read more here.

#5 Access to Prominent Force Measurement Experts

Every factor of quality listed above is realized and accomplished through a close and transparent relationship between customer and force measurement provider. Every application dictates a different force measurement solution. When we understand the application, we can select the right type of load cell or customize an off the shelf load cell to meet the quality and accuracy needs necessary for any project. This is why a customer’s access to a force measurement expert is an integral part of load cell quality.

Every force test and measurement project can create a different challenge and developing an accurate and reliable load cell to meet those challenges can be tough. Therefore, Interface considers these five factors, and hundreds more, for every product we engineer and build. This is our unwavering commitment to quality and customer satisfaction.

Contributor:  Ken Vining, Chief Engineer and Head of Quality

Strain Gages 101

A strain gage is a sensor that varies its resistance as it’s stretched or compressed. When tension or compression is applied, the strain gage converts force, pressure, and weight into a change that can then be measured in the electrical resistance.

At the heart and soul of every load cell is a strain gage. This is the pinnacle technology that allows engineers to collect and analyze force data. In the industry, it is known as force measurement.

Strain gages are made through a photo-etch process using a flexible backing and a very thin foil. The way a strain gage works is when the backing and foil stretches or compresses, resistance goes up and down respectively. We know this as force. Think of stretching like a three-lane highway switching to two lanes, and vice versa for compression with two lanes going into three. As the load cell’s internal strain gage experiences force, it sends a signal with a precise measurement of the amount of force it’s experiencing.

There are many different types of strain gages for a variety of environments and force measurement needs. The major difference in strain gages is the base material used in the manufacturing process. Different materials are used when a load cell needs to perform optimally in a variety of temperatures, humidity levels, and elevations. Matching the correct strain gage and a load cell to the customer’s needs is critical to accuracy.

“Here at Interface, we pride ourselves on developing the most accurate force measurement tools, and it starts with our proprietary manufacturing of the strain gage.”  Scott Dunne, Production Engineering Manager

More than 52 years ago, when our founder Richard F. Caris started Interface, he purchased over a mile of foil, which is the base material used in strain gages. Caris understood the only way to ensure Interface customers received quality results from their force measurement products was to control every aspect of engineering design, product development, and production.

The key ingredient to our precision accuracy and reliability is the fact that we have vertically integrated the entire manufacturing process from design to production and have a deep understanding of the materials necessary to suit every client’s need for optimal results

Many load cell makers purchase their strain gages from a third party. This means there’s more variability in their manufacturing process and you often find the variances in their materials clash and diminish the accuracy, or they are not correctly suited for the customer’s project requirements.  Interface makes all their own strain gages.

We have learned everything there is to know about strain gage manufacturing and can guarantee the quality of our load cells in any environment based on this tenured expertise and having manufactured and calibrated hundreds of thousands (ok, millions) of force measurement devices. And here’s a fun fact, although we’ve manufactured hundreds of thousands of load cells and strain gages, we haven’t even used half of the original mile of foil we purchased in 1968. Good product managed well can go a long way!

For more information on Interface’s commitment to accuracy and reliability, we have written The Load Cell Field Guide, the definitive resource on load cells. It is available on Amazon. You can also download our latest technical white paper, Contributing Factors to Load Cell Accuracy, for free by clicking here.

Contributor:  Scott Dunne, Production Engineering Manager, Interface