How Strain Gauges Work

Strain gauges, or sometimes known as strain gages, are basically instruments used to measure strain. Strain can be defined as being the amount of change seen in an object when a force or pressure is applied to it. When the object gets deformed because of an external pressure placed on it, then the measurement of this deformity or strain is the function of the strain gauge. Strain can also be caused by a lot of factors aside from applying a direct pressure on the object. This includes deviations in temperature, deviations in position, deviations in stability, and deviations in strength. Strain can be either be tensile or due to stretching which gives out a positive value, or compressive, which gives out a negative one. Either way, a strain gauge can still be used to measure its value.

The very first strain gauge was invented in 1938 by Ruge and Simmons, which was mainly made out of foil. This strain gauge is affixed in the object to be measured. As the object gets distorted, the foil also varies from its original length and position. This change is then measured and computed to be able to quantify it using the Gauge Factor, one of the parameters fundamentally assigned to measure the sensitivity of the strain gauge. The Gauge Factor is the ratio of the changes in resistance with the changes in strain. For metallic foil strain gauges, the gauge factor is usually known to be equal to 2.

There are also other types of strain gauges that have been made to measure the different strains produced by a variety of objects aside from the common strain gauge made out of foil. There is also the piezoresistors or the strain gauges that uses semiconductors, the best gauge to use to measure smaller quantities of strain, which also has a bigger gauge factor as compared to the foil strain gauge. There is also the mercury-in-rubber strain gauge that is used to measure the swelling in the target body part. To determine if cracks in the foundation are growing in size, then a mechanical strain gauge is used.

Several types of strain call for different types of strain gauges. But all strain gauges work according to only one principle, which is to measure the changes that occur physically with the object or objects for a certain period of time. You must first determine the best type of strain gauge to use for your measurement. When you have decided on which strain gauge to use, attach this device snugly on the object to be measured. This is so as to get an accurate measurement of the strain. As the object alters in shape and size, the change made is automatically detected and measured by the strain gauge. This is done by the transfer of strain made by the object to the strain gauge. A series of foil set in a network, sensitive to slight movements, detects the strain. The changes detected by the foil are then converted into a linear change in electrical resistance. This change is then detected as a percentage in electrical resistance. The detected resistance produced is then again measured and converted into the amount of strain perceived by the strain gauge.