A strain gage is a simple measuring system that determines the amount of strain, which is the displacement and deformation that results from an object under stress. It measures mechanical quantities by converting tension, force and pressure into an electrical signal.
Strain gages have another spelling that is commonly known; strain gauges. This load cell sensor type may vary in construction and measurement method. The most popular type is foil that is adhered to the object. Other kinds include semiconductor, bonded metallic wire, and carbon resistive.
When measuring the strain of an object, the temperature, material properties, the type of adhesive that bonds the gage to the object’s surface and the stability of the metal all affect the resistance.
Strain gages are used to detect cracking in machinery parts, as crack propagation, as an extensometer, to measure temperature, to measure residual stress, to gage shear modulus and as a transducer. It is a vital part of a load cell, which is a measuring device concerned with identifying and measuring compression, tension, and shear forces.
Another product that does the same thing and also makes use of strain gages is the force transducer, which is like a load cell except a more complicated system that is able to do the same thing plus measure a couple other aspects of an object as well. Industries that utilize these products include construction, general manufacturing, automotive, aerospace, and robotics.
There are three main types of strains that are measured by strain gages. Poisson strain is the thinning and elongation that occurs when a bar is strained. Bending strain is determined by measuring the relationship between the force and the amount of bending, which results from a twisting action. Shearing strain occurs when stress causes angular distortion of the object being measured.
The most common type of strain gage, made of foil and adhesive, has an insulating and flexible backing, which supports the metallic foil pattern. It is attached to an object by adhesives. As the object deforms, so does the flexible foil. The deformation of the foil causes the electrical resistance of the foil to change which then alters the signal output of the gage. The electrical output is measured and used to quantify the strains on the object.
When a strain gage is working as part of another system, like the load cells and force transducers mentioned above, multiple strain gages are used, connected by circuits. The formation of the strain gages is called the Wheatstone bridge equation, which was developed in the early eighteen hundreds.
Strain Gages Informational Video