A strain gauge is a sensor whose resistance varies with applied force. Applying outside forces to a stationary item causes stress and strain. It transforms various factors such as force, pressure, tension, and weight into a measurable change in electrical resistance.
It transforms factors like force, pressure, tension, weight, etc. into measurable changes in electrical resistance. Stress and strain are terms used to describe opposing internal forces within an object and the resulting displacement and deformation, etc.
In this reading, we’ll explore what a strain gauge is, its applications, parts, diagram, requirements, types, and how it works. We’ll also explore its advantages and disadvantages.
Let’s Begin!
What is a Strain Gauge?
When talking about strain gauges, it is important to first comprehend what they measure. A sensor known as a strain gauge measures electrical resistance that changes in relation to differences in strain.
Strain is the material’s displacement or deformation as a result of applied stress. are made to concentrate stress through beam elements where strain gauges are positioned.
The definition of stress is the division of the applied force to a material by its cross-sectional area. Strain gauges convert applied force, pressure, torque, etc. into measurable electrical signals.
Force causes strain, which the strain gauge measures by detecting a change in electrical resistance. We then collect the voltage measurement.
The strain gauge is a crucial tool in the electrical measurement approach that measures mechanical quantities. As their name suggests, they measure strain.
Technically, “strain” refers to a positive or negative sign that distinguishes between tensile and compressive strain. As a result, strain gauges may detect both expansion and contraction. An internal or external factor always causes a body’s stress.
Forces, pressures, moments, heat, changes to the material, and other factors may result in strain. The amount or value of the influencing quantity can be determined based on the measured strain value if certain requirements are met. Experimental stress analysis frequently uses this function.
Using the strain values found on the surface of a specimen (or structural part), experimental stress analysis tells us how stressed the material is and how safe and long-lasting it is.
We can create special transducers for the measurement of forces or other derived quantities, such as moments, pressures, accelerations, displacements, vibrations, and others. The pressure-sensitive diaphragm in the transducer typically has strain gauges bonded to it.
Related: What is a Pressure Gauge? Its Diagram and How it Works
Applications
Civil engineering and geotechnical monitoring commonly use strain gauges to identify breakdowns in structures such as bridges, buildings, and other structures.
We must constantly monitor these structures because any significant deformation could lead to injury or death.
These gauges are widely used because of their high precision, ability to perform at vast distances from the test object, and ease of setup and maintenance over long periods of time.
Testing in the outdoors is frequently not the same as testing in a lab under ideal conditions. Strain gauges are highly valuable due to their ability to function in harsh conditions and generate dependable, high-precision data.
A specialized gadget like a strain gauge is frequently required when an engineer tests products with irregular shapes in harsh locations with difficult-to-access setups.
For instance, aerospace applications use millions of strain gauges to verify the results of CAD (Computer-Aided Design) and FEA (Finite Element Analysis) simulations.
We frequently conduct these tests under dynamic conditions to provide a realistic portrayal of how various forces affect airplanes.
We also routinely use strain gauges for static testing. Some bridges use wireless telemetry to send the test results through Ethernet. On the other hand, we subject other bridges to visual inspection or penetrable testing to detect surface flaws.
While these technologies are cost-effective, they do not allow for continuous inspection, which can lead to catastrophic collapses like the I-35 Minneapolis steel truss bridge. The federal government designated the bridge as “structurally weak” in 1990, which meant it had to undergo yearly inspections.
The bridge eventually collapsed in 2007, killing 13 people due to a lack of continual strain gauge monitoring, significant repairs, or replacement. The following are the common applications of a strain gauge:
- Measurement of strain
- Measuring residual stress
- Vibration analysis
- Measurement of torque
- Measurement of bending and deflection
- Measurement of compression and tension
Requirement of Strain Gauge Material
A reliable strain gauge must be able to perform the following:
- The strain gauge should be modest in size and light in weight.
- It should be extremely strain-sensitive.
- The gauge factor of a strain gauge should be high.
- It must be simple to attach to the specimen.
- It should have a rapid response time and little time lag.
- It should be able to tell the difference between static, transient, and dynamic strain.
- It should be able to indicate and record information from a distance.
- Temperature, humidity, vibration, and other environmental factors should not affect it.
- It should be affordable, dependable, and readily available in a variety of sizes.
Diagram of a Strain Gauge
Types of strain gauge
There are several types of strain gauges available on the market. The following are the various types of strain gauges:
- Linear strain gauges
- Membrane Rosette strain gauges
- Double linear strain gauges
- Full bridge strain gauges
- Shear strain gauges
- Half-bridge strain gauges
- Column strain gauges
- 45°-Rosette (3 measuring directions)
- 90°-Rosette (2 measuring directions).
For measuring small strains, people generally prefer semiconductor strain gauges, also known as piezoresistive, over foil gauges. The gauge factor of a semiconductor gauge is usually higher than that of a foil gauge.
Semiconductor gauges are often more expensive, more temperature-sensitive, and more delicate than foil gauges. Strain gauges made of nanoparticles appear to be a promising new technique.
These resistive sensors, whose active area consists of an assembly of conductive nanoparticles like gold or carbon, exhibit a high gauge factor, a large deformation range, and low electrical consumption due to their high impedance.
Biological measurements, particularly blood flow and tissue swelling, use a mercury-in-rubber strain gauge. This strain gauge is made up of a little amount of liquid mercury encased in a small rubber tube that is wrapped around a toe or leg, for example.
When a bodily portion swells, it causes the tube to expand, making it both longer and thinner, increasing electrical resistance.
Fiber optic sensing can measure strain in conjunction with an optical fiber. One can conduct measurements at random locations along the fiber or at specific points. The 2010 America’s Cup boats Alinghi 5 and USA-17 use embedded sensors of this type.
Other optical techniques, such as electronic speckle pattern interferometry or digital picture correlation, can also measure strains.
MEMS frequently employs microscale strain gauges to monitor stresses caused by force, acceleration, pressure, or sound. Automobiles frequently use MEMS accelerometers to activate airbags.
As an alternative to piezo-resistant strain gauges (MOEMS), integrated optical ring resonators can monitor strain in microoptoelectromechanical systems.
Capacitive strain gauges use a variable capacitor to detect the degree of mechanical deformation.
Geotechnical and civil engineering applications use vibrating wire strain gauges. A vibrating, tensioned wire makes up the gauge. We calculate the strain by determining the wire’s resonance frequency, which increases with an increase in tension.
Geotechnical applications also use quartz crystal strain gauges. DART’s crucial sensor is a pressure sensor with a resonant quartz crystal strain gauge and a Bourdon tube force collector.
DART detects tsunami waves at the ocean’s deepest depths. When monitoring pressure at a depth of many kilometers, DART maintains a pressure resolution of approximately 1 mm of water.
How Does Strain Gauge Work?
The working of a strain gauge is quite interesting; it is less complex and simple to understand.
Now that we have developed the method of strain measurements, the next step in using strain gauges is to gather relevant data.We need to couple the strain gauge to an electrical circuit that can precisely react to the tiny resistance variations brought on by strain.
You can use several strain gauges in a divided bridge circuit to track minute changes in electrical resistance. A Wheatstone bridge is what you have here.
A Wheatstone bridge configuration delivers an excitation voltage across the circuit, and two points in the middle of the bridge measure the output voltage.
When there is no load on the load cell, the Wheatstone bridge balances and has zero output voltage. As the strain gauge deforms together with the material under it, even the smallest change causes a change in resistance.
The knockout of the bridge causes a change in the output voltage. As previously mentioned, the minute resistance change necessitates signal amplification for accurate identification of changes.
The amplification process boosts changes in the strain signal, but it also picks up extra undesired noise as a side effect. Signal conditioning removes the extra noise to produce accurate and understandable data.
Advantages and Disadvantages of a Strain Gauge
Advantages:
The following are the benefits of a strain gauge in its various applications:
- Because there is no moving part, there is no wear.
- Strain gauges are extremely accurate.
- It’s compact and low-cost.
- It has a wide frequency range.
Disadvantages:
- It’s a non-linear system.
- It is extremely temperature-sensitive.
- Regular calibration is required.
- You must manually apply strain gauges. It takes time and money to put them in their proper places. This is considered one of their most significant shortcomings.
Conclusion
A passive transducer, such as a strain gauge, transforms mechanical displacement into a change in resistance. A thin, wafer-like device, it measures applied strain and can connect to a variety of materials using an appropriate adhesive.
As the structure undergoes stress, the ensuing strain causes the strain gauge to deform. This article covers the definition, application, requirements, parts, diagram, types, workings, advantages, and disadvantages of a strain gauge.
