What Is A Strain Gauge? Understanding Its Function And Applications

A strain gauge is a tool for measuring the deformation of objects under stress. It provides key data for industries ranging from aerospace to civil engineering. This guide explores the working principles of strain gauges, their setup, and diverse applications. 

What Is a Strain Gauge?

Definition of a Strain Gauge

A strain gauge is a sensor used to measure the amount of deformation or strain experienced by an object when subjected to external forces. Invented in 1938 by Edward E. Simmons and Arthur C. Ruge, the device operates on the principle that the electrical resistance of a conductor changes when it is deformed. 

Typically, a strain gauge consists of a thin metallic foil arranged in a zigzag pattern mounted on an insulating flexible backing. This configuration allows it to measure strain across various materials and structures accurately.

The Basic Function of a Strain Gauge

The primary function of a strain gauge is to convert mechanical strain into an electrical signal that can be measured. When an external force is applied to an object, it causes deformation, which alters the length and cross-sectional area of the strain gauge. This change in dimensions results in a variation in electrical resistance, which is directly proportional to the amount of strain experienced by the object.

How Does a Strain Gauge Work?

A strain gauge operates based on the principle of the piezoresistive effect, where the electrical resistance of a conductor changes in response to mechanical strain. When an external force is applied to an object, it deforms, and this deformation affects the strain gauge attached to it. 

The gauge typically consists of a metallic foil pattern mounted on a flexible backing. This backing is bonded to the object's surface using an adhesive.

Principle Behind Strain Measurement

• Electrical Resistance Change

As the object deforms, the strain gauge experiences similar deformation, altering its length and cross-sectional area. This change in dimensions leads to a variation in electrical resistance, which the formula can quantify:

where R is resistance, L is length, and A is cross-sectional area.

• Gauge Factor

The sensitivity of a strain gauge is characterized by its gauge factor (GF), defined as:

where ΔR is the change in resistance, R is the original resistance, and ϵ is the strain. The relationship allows for precise measurement of strain based on resistance changes.

• Wheatstone Bridge Circuit

To measure these small resistance changes accurately, strain gauges are often integrated into a Wheatstone bridge circuit. This circuit consists of four resistive arms, with the strain gauge forming one arm. 

When deformation occurs, it causes an imbalance in the bridge circuit. This generates a voltage output proportional to the applied strain.

Strain Gauge Setup and Operation

• Installation: The surface where the strain gauge will be attached must be cleaned and prepared to guarantee good adhesion. Common adhesives include cyanoacrylate for short-term applications and epoxy for long-term installations.
• Connecting Wires: After bonding the strain gauge to the substrate, connecting wires are soldered to its terminals. This step may involve using protective tape during soldering to avoid damage to the gauge.
• Calibration and Testing: Once installed, it's important to calibrate the system and test for proper operation using an ohmmeter to check for correct resistance values. Calibration makes sure that measurements are accurate and reliable under expected operating conditions.

Where Are Strain Gauges Used?

Industrial Applications

Strain gauges are integral to weighing systems in manufacturing environments, truck weighing on highways, and silos that measure the weight of contents. They help maintain accurate measurements in applications like counting items based on weight. 

They also monitor stress in crushing machines to prevent damage from jams. These gauges are used to measure torque and power in drive shafts across various industries, including power plants and refineries. 

Aerospace and Automotive Utilization

In aerospace applications, strain gauges are bonded to structural components to measure stresses during flight. They are important for assessing wing deflection and making sure of the structural integrity of aircraft under various load conditions. Calibration is performed through ground tests using known load cells.

Strain gauges monitor stress in-vehicle components during performance testing. They help optimize vehicle designs for safety and efficiency. This is done by providing insights into material behavior under different conditions.

Civil Engineering and Medical Sector Implementation

Strain gauges are extensively used for structural health monitoring of bridges, buildings, and dams. They can be embedded within concrete or attached externally to monitor real-time strain and stress. They make sure of safety over a structure's lifespan. This application is vital for assessing load-bearing structures such as hospitals and skyscrapers.

In healthcare, strain gauges are utilized in devices like kidney dialysis machines, syringe pumps, and patient lift systems to monitor fluid flow rates and patient weight accurately. They also find applications in physical therapy devices that measure forces on joints.

Enhance your measurement precision with Load Cell Central’s expertise in strain gauge technology. From industrial weighing to structural monitoring, our solutions deliver accuracy and reliability for any application. 

Contact us today to discuss your project and discover the perfect strain gauge solution for your needs!