What is a Strain Gage?
Put simply, a strain gage is a sensing device used to measure strain on an object. Strain gages gather information about the degree of stress on the object and are thus used extensively in structural testing and monitoring applications, as in the testing of aircraft wing fatigue or monitoring pressure in medical infusion pumps to support patient safety. In addition to these applications, the strain gage serves as the building block for many types of transducers, including pressure, load, and torque sensors.
Advancements in Strain Gage Technology
While there are several ways of measuring strain, the most common one is using a bonded resistance strain gage, a device whose electrical resistance varies on proportion to the amount of strain in the device.
Today, the most widely used strain gage is the Advanced Sensors Technology bonded resistance strain gage. Micro-Measurements uses a precisely manufactured (in house) metallic foil to produce to resistive element providing for the best consistency and gage to gage matching available. The metallic strain gage consist of metallic foil arranged in a grid pattern. The grid pattern maximizes the amount of metallic foil subject to strain in parallel directions.
How does a strain gage measure strain?
Stress is calculated from information provided by the strain gage. Typically, a strain gage is attached to a structure and when such the structure is deformed (by tension, compression, or shear), the resistive strands in the strain gage follow the structural deformation, causing an electrical resistance change. The resistance change is then expressed in units of strain or stress.
Performance specifications to consider when searching for strain gages include operating temperature, the state of the strain (including gradient, direction, magnitude, and time dependence), and the stability required by the application.
The construction of a resistance strain gage involves bringing together the most effective electrical resistance material and backing and using optimal manufacturing and application practices.
A bonded resistance strain gage should meet the following criteria:
- Small size and mass.
- Agile development (ease of manufacturing in different resistance values, overall sizes, and measurement configurations)
- Durable, able to withstand handling and use
- Stability, repeatability, and linearity over a wide strain range
- Practical sensitivity to strain
- Ability to control effects of environmental variables like heat and cold
- Applicable for dynamic and static measurements and remote recording
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