The basic concept of strain, the working principle of the strain gauge, and the method of selecting the correct configuration type. In order to properly condition and collect strain measurements, in addition to understanding the characteristics of different strain gauge configurations, the required hardware must also be considered. For example, the voltage excitation required by strain gauges is only available on some conditioned measurement hardware. In order to better understand the measurement hardware required for strain measurement. And the application of strain principle in the pressure sensor.
Strain principle
In mechanical testing and measurement, it is necessary to understand how an object reacts to various forces. Strain refers to the amount of deformation of a material due to stress. People define strain as the ratio of the length change of the material to the original length, as shown in Figure 1. Strain can be either positive (tensile) or negative (compressive). When the material is compressed in one direction, it will extend in two other directions perpendicular to that direction, which is the Poisson phenomenon. Poisson's ratio (v) is a physical quantity used to reflect the phenomenon of cypress, which represents the negative value of the ratio of lateral strain to longitudinal strain. Strain has no dimension, but sometimes expressed in units such as in./in. or mm/mm. In reality, the strain value is very small.
The four different types of strain are: axial strain, bending strain, shear strain and torsion strain. Axial strain and bending strain are the most common strains (see Figure 2). Axial strain measurement materials are elongated or shortened by the horizontal linear force. The bending strain measurement material is elongated at one end and shortened at the other end by the linear force in the vertical direction. Shear strain measures the amount of deformation caused by linear forces in horizontal and vertical components. Torsion strain measures the ring tension of components in the horizontal and vertical directions.
There are many methods of strain measurement, the most common is the use of strain gauges. The resistance of the strain gauge has a proportional relationship with the strain of the device; the most commonly used strain gauge is the adhesive metal strain gauge. Metal strain gauges are composed of thin metal wires, or more commonly, metal foils arranged in a grid. The grid shape maximizes the amount of wire/foil strained in parallel directions. The grid is connected to a thin backplane called the substrate, which is directly connected to the test sample. Therefore, the strain on the test sample is directly transmitted to the strain gauge, causing a linear change in resistance.