What is a Strain Gauge and How Does it Work?

What do strain gauges measure?

The first thing to understand when discussing strain gauges is what they measure.  A strain gauge is a sensor whose measured electrical resistance varies with changes in strain. Strain is the deformation or displacement of material that results from an applied stress. Stress is the force applied to a material, divided by the material’s cross-sectional area. Load cells are designed to focus stress through beam elements where strain gauges are located. Strain gauges convert the applied force, pressure, torque, ect., into an electrical signal which can be measured. Force causes strain, which is then measured with the strain gauge by way of a change in electrical resistance. Then the voltage measurement is gathered using data acquisition.



How is strain measured?

Now that the process of strain measurements has been established, the next step when using strain gauges is getting useful data.The strain gauge must be connected to an electrical circuit that is capable of accurately responding to the minute changes in resistance associated with strain. Multiple strain gauges can be used in a divided bridge circuit to measure small changes in electrical resistance. This is called a Wheatstone bridge. In a Wheatstone bridge configuration, an excitation voltage is applied across the circuit, and the output voltage is measured across two points in the middle of the bridge. When there is no load acting on the load cell, the Wheatstone bridge is balanced and there is zero output voltage. Any small change in the material under the strain gauge results in a change in the resistance of the strain gauge as it deforms with the material. This causes the bridge to be thrown out of balance, resulting in a change in the output voltage. As stated earlier, the resistance change is minute, which means that signal amplification is often needed to properly determine changes. The amplification process strengthens the strain signal changes; however, it also leads to more unwanted noise also being detected in the signal. Signal conditioning filters out the excess noise, ensuring accurate and understandable data. 

wheatstone bridge strain gauge diagram

Michigan Scientific provides the resources required to get the best results from force and torque measurements. We produce single channel Strain Gage Amplifiers and multi-channel Strain Gage Amplifiers for our Slip Ring Assemblies. These amplifiers feature highly accurate bridge excitation, externally adjustable shunt resistance and gain, and remote bridge excitation On/Off capability. Our amplifiers create strong signals with minimal noise. Along with our products, our staff of highly trained technicians are capable of gauging a variety parts and applications. To learn more about our products or services, or to make an inquiry, contact Michigan Scientific today.


Featured image courtesy of Christian V. / CC BY.