Introduction

A strain gauge is like a smart sensor that senses changes in resistance when you apply force, pressure, tension, or weight. It helps convert these physical forces into electrical signals for measurement. When you push, pull, or press on something, it experiences stress and strain—stress being the inner resistance, and strain being the deformation. They are crucial tools in electrical measurements for mechanical quantities.

They specialize in measuring strain, which can be either stretching or compressing. Strain occurs due to various factors like forces, heat, or structural changes. By measuring strain, we can understand the impact of external influences on materials, predicting safety and endurance. In experiments, strain values on a surface help analyze stress and design transducers for measuring other factors like forces, moments, pressures, and more.

Working principle of strain gauge

A strain gauge works by using a thin wire or foil made of a conductive material attached to a flexible base. When the material experiences strain (like stretching or squeezing), the wire or foil changes shape, altering its electrical resistance. To measure this change, a Wheatstone bridge circuit is used. This circuit has four arms, with the strain gauge as one and fixed resistors as the others. When this gauge undergoes strain, it disrupts the balance in the Wheatstone bridge, creating a small electrical signal. This signal is proportionate to the applied strain.

By measuring this signal, we can determine how much strain the material is experiencing. This is useful for understanding mechanical properties like stress, load, and deformation in structures. They are commonly used in various fields like civil engineering, aerospace, automotive, and material testing.

Requirements of Strain gauge material

1. Small and Light:
   • They should be tiny and not add much weight to the object it’s attached to.
2. Super Sensitive:
   • It needs to be really good at sensing when the object it’s on gets stretched or squeezed (strain).
3. High Gauge Factor:
   • They should give a strong signal when there’s strain, making it easier to measure.
4. Easy to Stick On:
   • It should be simple to attach to different things for measuring strain.
5. Quick Response:
   • It should react fast when there’s a change in strain, without any delays.
6. Works for Different Strains:
   • It should be able to measure strain whether it’s steady, changing, or happening really fast.
7. Can Send Signals from Afar:
   • It should be able to send signals and data even from a distance.
8. Doesn’t Care About the Weather:
   • It shouldn’t get confused by things like temperature, humidity, or vibrations in the surroundings.
9. Affordable, Trustworthy, and Easy to Find:
   • It should be inexpensive, and reliable, and you should be able to get it easily in different sizes.

Types of Strain Gauges

Based on the Principle of Working:

1. Mechanical Strain Gauge:
   • This type of gauge relies on mechanical properties to measure strain or deformation in an object. It might involve physical components that change shape or position when subjected to strain.
2. Electrical Strain Gauge:
   • Electrical strain gauges use changes in electrical resistance to measure strain. As an object deforms, the electrical properties of the gauge, like resistance, change accordingly.
3. Piezoelectric Strain Gauge:
   • These gauges generate electrical charges in response to mechanical deformation. Certain materials exhibit piezoelectric properties, producing voltage when stressed.

Based on Mounting:

1. Bonded Strain Gauge:
   • Bonded gauges are attached or bonded to the surface of the object under observation. They stick to the material and deform along with it, allowing measurement of the strain.
2. Unbonded Strain Gauge:
   • Unbonded gauges are not directly attached to the object’s surface. They might be placed near the material but not bonded to it. They measure strain indirectly, often by detecting changes in the medium around the object.

Based on Construction:

1. Foil Strain Gauge:
   • Foil strain gauges are constructed using thin strips or foils of metal (often a special alloy) that undergo changes in electrical resistance when subjected to strain.
2. Semiconductor Strain Gauge:
   • Semiconductor strain gauges use semiconductor materials, which have properties that change with strain. The electrical characteristics of these materials vary as they experience deformation.
3. Photoelectric Strain Gauge:
   • Photoelectric strain gauges involve the use of light. They measure strain by detecting changes in the amount of light passing through or reflected by a material under deformation.

Applications of Strain Gauge

(i) Strain measurement: Monitoring material deformation.

(ii) Residual stress measurement: Assessing internal stresses post-manufacturing.

(iii) Vibration measurement: Analyzing oscillations in a system.

(iv) Torque measurement: Gauging rotational force.

(v) Bending and deflection measurement: Evaluating material flex and deformation.

(vi) Compression and tension measurement: Measuring forces causing material compression or tension.

Advantages of Strain Gauge

(i) No moving parts, so no wear and tear.

(ii) They offer high precision.

(iii) Small and cost-effective.

(iv) High-frequency bandwidth capability.

Disadvantages of Strain Gauge

(i) Exhibits non-linear behavior.

(ii) Highly sensitive to temperature changes.

(iii) Requires regular calibration.

(iv) Manual application of these gauges is time-consuming and costly, a significant drawback.

Frequently Asked Questions (FAQs)

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