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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