Types of Strain Gauges

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In 1938, the first bonded, metallic wire-type strain gage was introduced. The metallic foil-type strain gage is constructed of a grid of wire filament of approximately 0.001 in thickness, bonded directly to the strained surface by a thin layer of epoxy resin.

When a load is applied to the surface, it gets strained and experiences a change in length. This resulting change in length is conveyed to the resistor and the corresponding strain is measured in terms of the electrical resistance of the foil wire, which varies linearly with strain.

Other types of Strain Gauges are described below.

  1. Semiconductor Strain Gauges
  2. Thin-film Strain Gauges
  3. Diffused Semiconductor Strain Gauges
  4. Bonded Resistance Gauges
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Strain gauges are sensors that are used to measure strain or deformation in objects. They are commonly used in various fields, including engineering, material testing, and structural analysis. There are different types of strain gauges available, each with its own construction and working principles.

Here are some commonly used types of strain gauges:

1. Metallic Foil Strain Gauges:

  • Metallic foil strain gauges are the most widely used type of strain gauge.
  • They consist of a thin metallic foil (usually made of constantan or nickel-chromium alloy) that is bonded to a flexible backing material, such as polyester.
  • The foil is patterned in a grid-like structure, typically a Wheatstone bridge configuration, to measure strain.
  • When strain is applied to the object being measured, the foil undergoes deformation, causing a change in its electrical resistance.
  • This change in resistance is measured using a Wheatstone bridge circuit and is proportional to the strain experienced by the object.

2. Semiconductor Strain Gauges:

  • Semiconductor strain gauges are made from semiconductor materials like silicon or germanium.
  • They rely on the piezoresistive effect, where the resistance of the semiconductor material changes with applied strain.
  • Semiconductor strain gauges are compact and offer high gauge factors, making them suitable for measuring small strains.
  • They are often used in applications where high sensitivity and accuracy are required.

3. Bonded Resistance Strain Gauges:

  • Bonded resistance strain gauges are similar to metallic foil strain gauges but use a different construction technique.
  • Instead of a foil, they employ a resistive ink or paint that is applied directly to the surface of the test object.
  • The ink or paint contains conductive particles that create a resistive path.
  • When the object undergoes strain, the resistive path changes, causing a change in resistance that is measured to determine the strain.

4. Optical Fiber Strain Gauges:

  • Optical fiber strain gauges utilize the principle of fiber optic sensing to measure strain.
  • They consist of an optical fiber that is embedded or bonded to the object being measured.
  • Strain applied to the object causes changes in the optical properties of the fiber, such as length or refractive index, which are detected and measured.
  • Optical fiber strain gauges offer benefits such as immunity to electromagnetic interference and the ability to measure strain in high-temperature or hazardous environments.

These are some of the commonly used types of strain gauges. The selection of a particular type depends on factors such as the application requirements, sensitivity, temperature range, and budget considerations.