What is Strain Gauge?
A Strain gauge is a sensor whose resistance changes with applied force; it converts force, pressure, tension, weight, etc., into a variation in electrical resistance which can then be quantified. When external forces are applied to a stationary object, stress and strain ensue. Stress refers to the object’s internal resisting forces, while strain denotes the displacement and deformation that occur.
The strain gauge is one of the most critical tools in the electrical measurement technique used for assessing mechanical quantities. As their name suggests, they are employed for the measurement of strain. Technically, “strain” encompasses both tensile and compressive strain, indicated by a positive or negative sign. Therefore, strain gauges can detect both expansion and contraction.
The strain on a body is always induced by an external influence or an internal effect. Strain might result from forces, pressures, moments, heat, structural changes in the material, and similar factors. If certain conditions are met, the magnitude or value of the influencing factor can be determined from the measured strain value. This feature is extensively utilized in experimental stress analysis. Experimental stress analysis employs the strain values measured on the surface of a specimen or structural part to determine the stress within the material and predict its safety and endurance. Special transducers can be engineered for measuring forces or other derived quantities, such as moments, pressures, accelerations, displacements, vibrations, and more. The transducer typically contains a pressure-sensitive diaphragm with strain gauges attached to it.
Discover more about strain gauges
Precision Strain Gauges for General Applications
Precision strain gauges for general purposes are enclosed constantan foil strain gauges available in a diverse range of designs suitable for scientific, industrial, and experimental stress analysis. These precise strain gauges can be utilized for monitoring industrial equipment in experimental stress analysis or various scientific applications. In the general-purpose strain gauge section, you’ll find the strain gauge designs alongside the part numbers, allowing you to visualize the geometry of the strain gauge. The gauge dimensions are also provided in both SI (Metric, mm) and US Customary (English, inches) units. General-purpose precision strain gauges are presented in linear designs, dual parallel-grid designs, Tee rosettes (0/90°), rectangular or delta (45° or 60°), stacked or planar rosettes, and shear designs.
High-Quality Strain Gauges for Transducers
High-quality strain gauges tailored for transducers are designed for customers engaged in manufacturing transducers or similar sensing devices. These strain gauges feature stricter tolerances on the carrier trim dimensions, allowing the carrier edge to be utilized for strain gauge alignment if necessary. They also boast tighter tolerances on nominal resistance values. These gauges can be adjusted for creep to adhere to a transducer manufacturer’s specifications, and they can be customized to meet the specific requirements of a transducer. Additionally, they serve as excellent gauges off-the-shelf for experimental stress analysis and/or strain verification projects.
Karma Strain Gauges
Omega offers a comprehensive range of Karma strain gauges. These strain gauges are suitable for a variety of static and dynamic applications. Karma strain gauges are ideal for transducer applications requiring long-term stability or operation at elevated temperatures. At room temperature, for static strain measurements, these transducers maintain excellent stability for months or even years. Additionally, Karma strain gauges are recommended for static strain measurements over a broad temperature range from -75 to 200°C (-100 to 392°F) due to their good linearity across this wide temperature range. They are often employed in fatigue-rated transducer designs, as the fatigue life of the Karma alloy generally surpasses that of constantan. Therefore, transducers utilizing Karma strain gauges offer superior fatigue life. Karma, a nickel-chromium alloy, was chosen as a strain gauge material for its modulus-compensating properties, which significantly reduce span shift in transducer design. With Karma alloys, the gauge factor tends to decrease as temperature increases, and this reduction in elastic modulus helps minimize span shift. However, Karma alloys present some challenges, such as difficulty in soldering without special fluxes. OMEGA resolves this issue by providing Karma strain gauges with copper-plated solder pads, eliminating the need for special flux or procedures.
Bonded Foil Strain Gauges
The first bonded metallic wire-type strain gauge was invented in 1938. The metallic foil-type strain gauge consists of a wire filament grid (a resistor) approximately 0.001 in. (0.025 mm) thick, bonded directly to the strained surface with a thin layer of epoxy resin. When a load is applied to the surface, the resultant change in surface length is transmitted to the resistor, and the corresponding strain is measured as a change in the electrical resistance of the foil wire, which varies linearly with strain. The foil diaphragm and the adhesive bonding agent must function together to transmit the strain, and the adhesive must also act as an electrical insulator between the foil grid and the surface. When selecting a strain gauge, one must consider the strain characteristics of the sensor as well as its stability and temperature sensitivity. Unfortunately, the most desirable strain gauge materials are also sensitive to temperature changes and tend to alter resistance over time. While this may not pose a significant issue for short-duration applications, continuous industrial measurement necessitates temperature and drift compensation.
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