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Strain gauges are vital components used in various sensors to measure deformation or strain under different loads or stresses. These are either directly integrated into sensor units or used in modular configurations where they are connected to external systems or surfaces. These types are:
This type consists of fine wire, typically made from copper-nickel alloys, arranged in a specific pattern. The wire is bonded to a backing material and often used in high-temperature applications, such as aerospace and foundries. In these harsh conditions, durability is vital, and while they are flexible and easy to install in the lab, they require high expertise to install correctly in the field and to produce accurate measurements.
The most widely used strain gauge is the foil strain gauge. It consists of a thin metallic foil etched into a wire-like pattern. Common materials for these foils are constantan (copper-nickel) and nickel, as they exhibit great resistance to strain. The configuration is known to offer high sensitivity and stable long-term performance. The backings are made from plastic, metal, or paper and are adhesive-coated for bonding to surfaces. A common use of these strain gauges is in load cells, torque sensors, pressure sensors, and structural health monitoring.
These advanced strain gauges are fabricated using semiconductor materials like silicon. They provide significantly higher sensitivity than wire or foil configurations. These strain gauges are commonly used in applications for measuring tiny strains and where limited space is available. The micro strain gauge can also be found in the pressure transducer, MEMS accelerometer, and force sensors, where precision is key.
Semiconductor strain gauges have better sensitivity than metallic gauges. They offer gauge factors up to 1000, depending on the material and doping concentration. They are usually made from silicon, but in some cases, germanium and gallium arsenide are used. These gauges are sensitive to temperature and have a nonlinear response. They measure minute strain levels in specialized applications and have good sensitivity. These strain gauges are also found in pressure sensors, torque transducers, and displacement sensors to measure micro strain levels.
The performance of strain gauges directly impacts the accuracy and reliability of measurements in any given application. These are some vital features that should be considered:
The gauge factor describes the sensitivity of the strain gauge and is the ratio of the relative change in resistance to the relative change in length. Therefore, the greater the strain gauge factors, the more sensitive it will be to small deformations, and semiconductor strain gauges have the greatest sensitivity. In practice, this means that strain gauges with high sensitivity are capable of detecting minor variations, which is critical in fields like biomedical engineering, aeronautics, and materials testing, where tiny strains can assume gigantic significance.
Temperature affects strain gauges, which can change their reading. Therefore, for this reason, many strain gauges have materials with high thermal stability and can reliably work in extreme temperatures. Wire strain gauges are one of the examples of a high-temperature application in the aerospace industry or in furnace and environmental equipment in foundry. Besides, some gauges have temperature compensating circuits integrated with them to ensure they remain unaffected by temperature fluctuations.
Proper bonding is critical for strain gauge performance. This is because any air bubbles or misalignment will lead to inaccurate readings. Strain gauge adhesives are majorly used to bond the gauges to the substrates. However, they should be selected based on temperature, environmental, and substrate material applications. Also, selection is important since differences in the coefficient of thermal expansion between the strain gauge and surface cause stress at the interface.
The resistance change in strain gauges is typically generated by the material being stretched or compressed. Most foil strain gauges on the market use constantan or platinum-nickel alloys because they offer consistent electrical resistance and can withstand mechanical fatigue in a longer time. Also, given their flexibility, they can be precisely bonded to curved surfaces, thus capturing strain on a wide variety of geometries and profiles. This material compatibility and flexibility make strain gauges essential for maintaining durability in many applications.
When strain gauges are used in combination with other electronic components, they find many applications. Highlighted below are some of the common use cases:
Live monitoring of critical structures for safety and maintenance purposes is done through the application of strain gauges. For instance, bridges, buildings, and dams can have built-in strain gauges to detect deformation over time, showing whether a structure has stress beyond safety margins. This allows proactive repair or reinforcement actions to be taken before failure. In such a case, a strain gauge pressure transducer is important in continuous data transmission, enabling real-time assessment and early detection of potential issues.
In the aerospace and automotive industries, the performance and safety of aircraft, space vehicles, and car designs are tested using strain gauges. Gauges are mounted on critical components like wings, fuselage, engines, and chassis to understand how materials react under normal and extreme operating conditions. The data measured allows engineers to validate design integrity, optimize material usage, and improve future designs. This ensures absolute vehicle performance, safety, and reliability.
Measure applied force or weight in a specific system is the function of strain gauge load cells. Such load cells can be found in industrial scales, weighing the cargo and materials in the center, measuring the force in mechanical testing equipment, and monitoring critical safety in elevators and lift systems. In these applications, strain gauges convert physical deformation under load into electrical signals. These signals are processed to give precise measurement and mathematical estimation of weight or force.
Strain gauges measure the mechanical deformation of a diaphragm in pressure sensors or transducers under applied fluid pressure inside a sealed cavity. This application is seen widely in industrial automation and control systems. Herein, strain gauges are applied to monitor pressure in pipelines, hydraulic systems, and chemical reactors. Further, they can be used in medical devices to track blood pressure in patients and automotive systems for measuring manifold pressure.
Rotational force, which is the product of the torque, is measured by strain gauge torque transducers fitted within shafts or couplings. Further, they are critical in assessing torque in motor systems, monitoring the performance of mechanical assemblies, and preventing overloading in industrial machinery. In the field of motorsport, they are used for real-time engine performance evaluation. In this strain gauge can provide accurate and non-intrusive torque monitoring without affecting system operation.
Several factors come into play when selecting strain gauges for particular applications. Some of these factors include:
Understand the specific needs of the intended application. This includes measuring desired strain magnitude, surface conditions, environmental factors, and temperature range. For example, in monitoring structures, long-term stability is important, while in dynamic testing, fast response is critical. Knowing these requirements helps in selecting the right strain gauge, such as a foil, wire, or semiconductor gauge, which suits typical strain conditions for the application.
To detect small strain measurements, highly sensitive strain gauges are required, such as in semiconductor strain gauge applications. These strains are usually in the range of microstrain. Great sensitivity is not always better, as high-gain amplification might be needed, leading to increased noise susceptibility. Balance the required strain measurement against sensitivity to determine the proper strain gauge factor.
Consideration of the material that makes up the substrate where the strain gauge will be bonded is a must. Materials in the form of metals, plastics, composites, or ceramics possess different coefficients of thermal expansion (CTE). Take, for example, the temperature variation. There will be a mismatch between the strain gauge and surface if there is a significant mismatch. This will affect the strain measurement. To eliminate this issue, use a strain gauge that is compatible with the substrate in the temperature range of the application.
Foil strain gauges are best suited for applications with limited temperature ranges and are stable over time. Other gauges, like wire strain gauges, are best in excess-temperature applications. These gauges provide stable readings under extreme heat. Temperature is a vital factor affecting strain gauge performance. Changes in temperature lead to changes in resistance, which will be mistaken for strain. Therefore, to reduce this effect, one must select a strain gauge with a high level of thermal stability and use temperature-compensating techniques.
The technique for bonding the strain gauge to the substrate affects its performance. For example, the strain gauge measures inaccurate values if the adhesion process has air bubbles or misalignment. Therefore, ensure that the bonding material selected is suitable for the environment and substrate surface where the strain gauge will be applied. Also, proper surface cleaning and preparation will improve the accuracy of strain measurement.
A1: A strain gauge works based on the principle of resistance variation. When the gauge is deformed, stretched, or compressed, its electrical resistance changes. This is because the wire or foil lattice is elongated or compressed. The amount of resistance change is proportional to the strain amount it experiences. Strain gauges have a gauge factor, which is the ratio of resistance change to mechanical strain. Further, this proportionality allows strain gauges to detect minute deformations in mechanical structures under load and find applications in measuring force, pressure, and displacement.
A2: Strain gauges find applications in various industries. These industries include aerospace, structural monitoring, and electronic device testing. More often, they are used in load cells to measure weight and force in industrial automation. Also, they measure pressure in hydraulic systems and automotive sensors. Other common places are torque sensors for rotating machinery. These are also extensively used in research and development to measure material properties. In this case, they help in evaluating stress and strain in experimental setups. Basically, their versatility makes them important in preventive maintenance, quality control, and system design.
A3: Several factors affect the choice of strain gauges in industries. Some of these factors include operating temperature, environmental conditions, expected strain range, and surface characteristics of the substrate. Other factors include response time, previous stability, and ease of installation. For example, wire strain gauges are suited for high-temperature environments. On the other hand, semiconductor gauges are appropriate where high sensitivity will be needed. In harsh conditions, protect the strain gauges from contaminants using a protective layer. The protective layer, however, should not affect the gauge's sensitivity.
A4:Strain gauges require little maintenance. However, regular inspection for external damage, degradation of the protective layer, and checking for water or dust infiltration will improve reliability. Furthermore, monitoring drift in calibration and early replacement of damaged strain gauges will enhance their longevity. Also, one must ensure proper surface preparation before installation of any new strain gauges to improve long-term performance.
