Strain gauging is performed in order to validate design of a structure with conformance to a specific standard. It is to measure the strain level at the crucial position where concentrated loading is acting on during operation and evaluate the stress coming out of it. This measurement is vitally important for product design and safety.

Structural deformation, compression, tension and torque can be measured accurately using strain gauge technology and widely applied in various applications. Let’s observe the principles, accuracy factors and benefits of strain gauge for monitoring and ensuring the structural integrity including different configurations like Full Wheatstone Bridge, Quarter Bridge, Half Bridge, Rosette and Concrete Gauge.

The principles of strain gauge lies on detecting and measuring the electrical resistance changes in response to strain or deformation experienced by a structure. Strain gauges are sensors that work in this principle by converting the change in resistance into measurement of strain or stress. This gives valuable insight into the behavior of any structure.

Next, accuracy is affected by several factors and those factors must be considered to ensure accurate measurements:

1. Calibration: Accurate calibration is essential to obtain a calibration curve. This involves comparing the output of the strain gauge with actual known reference load or strain. It is necessary to regular recalibration to maintain accuracy over time.
2. Installation: Proper installation of strain gauges is crucial for accurate measurements. It needs careful and meticulous work to attach the strain gauge at specified location by following the manufacturer guidelines. Controlling thermal effects and minimizing external influences is critical for precise readings.
3. Environmental Conditions: Accuracy can be affected environmental factors such as humidity, temperature and vibrations. These conditions should be taken to account during data analysis and planning for the time of design of any system.
4. Strain Gauge Quality: Quality of strain gauge surely affected the accuracy. High quality strain gauges manufactured with tight tolerances and precision provide more reliable and accurate measurements.
5. Data Acquistion and Analysis: The accuracy of measurements depends on the quality of the data acquisition system and the analysis techniques employed. Properly calibrated equipment, signal conditioning, and appropriate filtering contribute to accurate results.

Strain gauge has variation of configurations to suit different measurement requirements. Some common configurations include:

• Full Wheatstone Bridge: This configuration uses four strain gauges in a bridge arrangement, providing a highly precise measurement of strain or stress. It offers improved sensitivity and accuracy but requires a more complex data acquisition system.
• Quarter Bridge: In this configuration, a single strain gauge is used along with three fixed resistors to create an unbalanced bridge. It is a simpler and cost-effective option for measuring strain, but it provides relatively lower accuracy.
• Half Bridge: This configuration uses two strain gauges along with two fixed resistors. It offers a balance between accuracy and simplicity.
• Rosette: A rosette configuration consists of multiple strain gauges arranged in different orientations to measure strains in multiple directions. This allows for a more comprehensive analysis of the structural behavior.
• Concrete Gauge: Specifically designed for concrete structures, concrete gauges are strain gauges encapsulated in materials that can bond well with concrete. They enable accurate measurement of strains in concrete elements, providing insights into their structural performance.

With its different configurations, strain gauge technology offers plenty of benefits and finds applications in various industries:

• Safety Assurance: By monitoring structural deformations resulting from load, pressure, or tilt, strain gauges provide vital data to ensure the safety of workers, occupants, and equipment. Unusual variations in these parameters can be detected to prevent severe damage.
• Versatility: Strain gauges can be used individually or simultaneously on various equipment and structures such as forklift trucks, cranes, bridges, floors, and more. This versatility allows for monitoring and analysis in numerous applications, providing valuable insights into structural behavior.
• Sensitivity and Precision: Strain gauge technology, regardless of the configuration used, offers high sensitivity and precision. This enables accurate measurements of even minute structural changes and strains, providing valuable data for analysis and decision-making.
• Easy Installation: Strain gauges are designed to be user-friendly and easy to install. They can be applied to solid structures without requiring major modifications, minimizing downtime, and allowing for efficient implementation.

While it holds many benefits, it also has several challenges in installing and handling of strain gauges on structures which may potentially leading to accuracy and precision issues. Some common challenges are:

• Surface Preparation: Proper surface preparation is crucial for strain gauge installation. The surface should be clean, free from contaminants, and properly roughened or smoothed depending on the adhesive requirements. Inadequate surface preparation can result in poor bonding and compromised accuracy.
• Adhesive Bonding: Achieving a strong and reliable bond between the strain gauge and the structure is essential. Improper adhesive application, insufficient curing time, or using the wrong adhesive can lead to bonding failures, affecting the accuracy of the strain measurements.
• Temperature Compensation: Temperature changes can influence the accuracy of strain gauge measurements. Thermal effects on the structure can introduce strains that are unrelated to the measured loads. Proper temperature compensation techniques, such as using dummy gauges or compensation formulas, need to be employed to account for these effects.
• Electrical Noise and Interference: Electrical noise and interference from external sources can negatively impact the accuracy of strain gauge measurements. Shielding the measurement circuitry, using proper grounding techniques, and minimizing electromagnetic interference sources are important considerations to ensure reliable and accurate data.
• Structural Dynamics: In dynamic applications where structures experience rapid or cyclic loading, the dynamic response of strain gauges must be considered. Strain gauges have limitations in capturing high-frequency events, and their response may be affected by factors like natural frequency and resonance. Appropriate filtering and signal conditioning techniques are required to address these challenges.
• Environmental Factors: Environmental conditions, such as temperature variations, humidity, and corrosive environments, can affect the performance of strain gauges and their adhesives. Understanding and mitigating these environmental factors are crucial to maintaining accuracy and reliability over time.
• Calibration and Recalibration: Strain gauges require regular calibration to maintain accuracy. Failure to perform regular recalibration can result in drifting and inaccurate measurements. Adhering to the recommended calibration intervals and procedures is essential to ensure reliable and precise strain measurements.

Here is how we do the strain gauge installation

Strain Gauge Installation

Installation of strain gauge requires careful and meticulous work. Every details need to be followed to obtain a reliable accurate data measurement. Followings are the installation method of strain gauge:

1. Locations of Strain Gauge

Locations of strain gauges are determined by the design and structural engineers. The points of measurement are where the deformation is considered to be crucial and has the has the highest stress in the analysis. The locations are marked on the structure for later detail work. Additionally, the engineer should have several points tested by simulation using CAE software for structure, such as FEMtools, and will be comparing them with actual readings obtained from strain gauge testing. Comparison results will determine the safety of the structure.

2. Surface Preparation

The appointed locations of strain gauge are surface finished as the marked area is grinded, removing coating layers and smoothed uneven surface until flat and shine. Better surface gives better bonding, thus affecting good quality to the measurement.

3. Gauge Attachment

After surface preparation has finished, the surface is then cleaned with isopropyl alcohol to remove the dust and stains. Afterwards, the exact location of strain gauge will be drawn ensuring the positioning of the strain gauge on the structure is accurate. Then, the strain gauge is bonded to the surface using cynoacrylate glue, epoxy or other type of adhesive bonding agent depending on the surface type.

4. Wiring

Cable length will be determined based on the drawing given. The cable is either soldered to the strain gauge or alternatively crimped to a connector for connection to the strain gauge depending on the situation. After the strain gauge attachment has finished, the cable will be laid towards the data acquisition system. The cable is laid along the structure while making sure safety and tidiness is followed to prevent accidents.

5. Protective Coating

Finally, protective coating is applied to prevent accidental damage to the strain gauge.