What is a Strain Gauge?
In the field of electronic components and sensor technology, the strain gauge is a fundamental sensor that converts mechanical strain into electrical signals. Its output is typically measured with high precision using a Wheatstone bridge circuit. Whether in industrial automation, load measurement, weighing systems, material mechanics testing, or structural health monitoring, strain gauges and bridge circuits form the core of modern strain measurement systems. This article provides a systematic introduction from key perspectives such as definition, working principle, structure, and bridge connection methods.
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IV. Strain Gauge Bridge Connections
I. What is a Strain Gauge?
A strain gauge is a resistive sensor used to measure the strain produced in materials or structures under force. Its basic function is to convert tiny resistance changes caused by mechanical deformation into measurable electrical signals. It is widely used to measure changes in physical quantities such as force, pressure, torque, and displacement, making it an important type of sensor.
II. Working Principle
The principle of a strain gauge is that its resistance changes as the material deforms. When an object is subjected to external force, its shape and size change, causing the strain gauge to experience stretching or compression. Since strain gauges are made of conductive materials, their resistance changes in response to strain. This resistance variation can be measured and analyzed using a suitable bridge circuit.
III. Structure
Strain gauges are made from metal or semiconductor materials and usually take the form of thin sheets or fine wires. Common materials include alloys like Constantan, such as Constantan No. 4, copper-zinc alloys, and single-crystal silicon. Strain gauges are typically manufactured either by hand or with automated equipment, achieving high precision and stability.
IV. Strain Gauge Bridge Connections
There are two common ways to connect strain gauges in a bridge circuit: the quarter-bridge connection and the full-bridge connection.
1. Quarter-Bridge Connection
In a quarter-bridge connection, the strain gauge forms one resistor of a bridge circuit, while the other three resistors are either fixed known resistors or adjustable resistors made with voltage-stabilized diodes. When the object is subjected to an external force, the resistance of the strain gauge changes, unbalancing the bridge. By measuring the voltage difference in the unbalanced bridge, the force applied to the object can be calculated.
2. Full-Bridge Connection
In a full-bridge connection, two of the four resistors in the bridge are strain gauges. This configuration increases the sensitivity and stability of the bridge. When the object experiences force, the resistances of the strain gauges change, causing the bridge to become unbalanced. By measuring the voltage difference at this unbalanced state, the force acting on the object can be determined. Compared to the quarter-bridge, the full-bridge provides more accurate measurement results.
V. Conclusion
Strain gauges are indispensable components in electronic measurement and sensing. By converting mechanical strain into resistance changes, they provide a core method for precise measurement of force, pressure, displacement, and other physical quantities. Because the resistance changes are extremely small, measurements usually rely on the precise balance and unbalance output of a Wheatstone bridge circuit. Depending on measurement needs and performance requirements, either quarter-bridge or full-bridge connections can be used to optimize sensitivity, stability, and temperature compensation. In modern industrial automation, aerospace, material testing, and structural monitoring, strain gauge–based bridge measurement systems play a fundamental but critical role.
