What is a strain gauge bridge and how does it work?

By Cristian V. - Own work, CC BY 4.0, Link

The strain gauge (DMS) bridge is an essential instrument in metrology, used to measure mechanical deformations in materials and components. It is based on the principle of electrical resistance change, which occurs when a material is stretched or compressed. This technology is widely used in industry, particularly in force, pressure, and strain measurement.

Basics of the Strain Gauge Bridge

A strain gauge bridge consists of multiple strain gauges arranged in a so-called Wheatstone bridge. This electrical circuit enables highly precise detection of small resistance changes caused by mechanical deformation. Main components of a strain gauge bridge:

• Strain gauge (DMS): Sensors attached to a substrate whose electrical resistance changes when stretched.
• Wheatstone bridge: An electrical circuit consisting of four resistors that can measure changes in resistance values.
• Power source: Provides electrical voltage within the bridge circuit.
• Measuring device: Detects changes in bridge voltage and converts them into measurable values.

Functionality of the Strain Gauge Bridge

The functionality of a strain gauge bridge is based on the deformation of a material to which the strain gauge sensors are adhered or otherwise attached. This deformation leads to a change in the electrical resistance of the strain gauge. The Wheatstone bridge converts these resistance changes into a voltage that can be measured and analyzed. Measurement principle:

1. When the component is loaded, its shape changes slightly.
2. The strain gauge undergoes elongation or compression.
3. This strain causes a change in electrical resistance.
4. The Wheatstone bridge amplifies this change and converts it into a voltage.
5. The voltage is converted into a physical quantity, such as force or pressure.

Types of Bridges in Strain Gauge Technology

There are different configurations of the Wheatstone bridge, which vary in terms of sensitivity and compensation properties:

Bridge Type	Description	Advantages
Quarter Bridge	Only one active strain gauge, the remaining resistors are fixed references.	Simple design, cost-effective
Half Bridge	Two active strain gauge sensors that complement each other.	Higher sensitivity, temperature compensation
Full Bridge	All four resistors are strain gauge elements.	Highest accuracy, low interference

Applications of the Strain Gauge Bridge

Strain gauge bridges are used in many areas of industry. They are particularly applied where forces, strains, or pressures need to be measured precisely:

• Mechanical engineering: Load analysis on components and materials.
• Aerospace: Fatigue testing and structural analysis.
• Automotive industry: Crash tests and load measurements on vehicle structures.
• Medical technology: Sensors for prosthetics and orthotics.
• Civil engineering: Monitoring the structural integrity of bridges, tunnels, and buildings.

Advantages and Challenges

The strain gauge bridge offers numerous advantages that make it an indispensable tool in metrology. However, there are also challenges to consider when using it.

Advantages	Challenges
High sensitivity and precision	Requires complex calibration
Direct conversion of strain into electrical signals	Temperature influences must be compensated
Use in various materials and environments	Mechanical attachment requires care
Compact design and lightweight	External interference can affect measurement results

Conclusion

The strain gauge bridge is a precise and versatile method for measuring mechanical loads. Its high sensitivity and adaptability make it an essential technology in many industrial sectors. Despite some challenges, such as temperature drift or calibration effort, the advantages significantly outweigh them, especially in applications requiring the highest accuracy. Whether in mechanical engineering, aerospace, or medical technology – the strain gauge bridge remains an indispensable tool for precise measurement of mechanical deformations and forces.