How to Measure a Strain Gauge
There are several ways to measure strain. The most common is to use a strain gauge. In laymen’s terms, a strain gauge is a device whose electrical resistance varies in proportion to the amount of strain in the device. The preferred type is a bonded metallic strain gauge. A critical operation in measuring strain is the ability to properly bond the strain gauge to the item under test.
The strain gauge has been used for many years. It is a fundamental element used for load sensors, pressure sensors, torque sensors, and also for position sensors. While there are many types of strain gauges, the foil type represents a good example. The principle is simple: The foil used is subjected to various amounts of pressure that will change the foil in defined ways.
Material Required
Strain Gauge
Foil
Varying electrical resistances
Keep in mind that if a strip of a conductive metal is stretched, it will naturally become thinner and longer. These dimensional changes will in turn, increase the electrical resistance of the metal strip. In reverse order, if the strip of metal is placed under a force that will compress it, this will broaden the piece and hence result in shortening the strip. Basically, that’s how to measure strain. The strain gauge is a small diameter wire folded in a pattern within itself. These gauges can be acquired commercially and are generally equipped with resistance values from 30 to 3000 ?.
A general description
A strain gauge can also be described as a device consisting of extremely fine wire, referred to as metallic foil, laid out in a grid fashion. It is bonded to a carrier. The parallel foils in the grid design optimize measurement of strain, while the tightness of the grid cross-section results in the minimization of shear strain.
The foil grid is attached to the carrier. Specimens in to be tested are attached directly to the carrier, enabling the strain of the specimen to be directed. This is accomplished by directing the strain of the object to the strain gauge, which in turn will indicate the change in electrical resistance.
The strain gauge is sometimes used in conjunction with a resistive bridge network. This bridge networks detects the strain gauge resistance and then amplifies it. The differences of resistance in the strain gauge are proportional to specimen elongation due to the stresses applied.
This change in resistance can be measured with a table of measurement or automated through a computer-generated spreadsheet or graphing. Keep in mind that this measurement can then be translated into the PSI (pounds per square inch) experienced by the specimen under stress. In conclusion, there are many manufacturers who supply all the necessary strain gauges and materials from connection tags, to binding adhesives and training.