sensors

Foil Based Strain Gauge

High-frequency resistive sensor for dynamic strain measurement and fatigue analysis in structural steel and machinery.

Nominal Resistance
120 Ω or 350 Ω
Gauge Factor
Approx. 2.0
Strain Range
±3% (30,000 µε)

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Overview

High-frequency resistive sensor for dynamic strain measurement and fatigue analysis in structural steel and machinery.

The Geolook Foil Based Strain Gauge is a precision resistive sensor designed for capturing dynamic strain and rapid loading events. While Vibrating Wire sensors are ideal for long-term static monitoring, foil gauges are the industry standard for high-speed data acquisition. Consisting of a photo-etched metallic foil pattern on a flexible polyimide carrier, these gauges are bonded directly to the structure using specialized adhesives. They provide an instantaneous change in electrical resistance proportional to the mechanical strain, making them capable of monitoring vibrations, impacts, and high-frequency fatigue cycles.

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Benefits & Features

  • Ultra-fast response time for dynamic events
  • Available in Linear, Rosette, and Shear patterns
  • Minimal mass (does not affect specimen dynamics)
  • Self-temperature-compensation (STC) for steel or concrete
  • High gauge factor for excellent sensitivity
  • Compatible with high-speed Wheatstone bridge loggers
  • Extremely low profile for installation in tight spaces

Detailed Description

The Physics of Resistive Strain

Foil gauges operate on the principle of piezoresistivity. When the structure to which the gauge is bonded undergoes deformation, the foil grid stretches or compresses.

This physical deformation changes the electrical resistance of the foil. By measuring this resistance change through a Wheatstone bridge circuit, engineers can calculate the exact strain with nanosecond-level response times.

Wheatstone Bridge Configurations

Because the resistance change is very small, specialized bridge-completion is required. We offer support for three primary configurations:

  • Quarter Bridge: Single gauge measurement; common for general stress analysis.
  • Half Bridge: Two gauges; used for bending compensation or sensitivity enhancement.
  • Full Bridge: Four gauges; provides maximum accuracy and automatic temperature compensation for torque or axial load measurement.

Installation: The Bond is Everything

For a foil gauge, the adhesive is part of the sensor. The G77-F150 requires meticulous surface preparation, including degreasing and abrading the parent material.

Once bonded with cyanoacrylate or epoxy, the gauge must be environmentalized using a protective coating (wax, silicone, or rubber) to prevent moisture from causing 'zero-drift' or corrosion of the delicate foil grid.

Dynamic vs. Static Choice

If your project requires monitoring a dam for 50 years, use our VW gauges. However, if you need to know the strain in a bridge girder at the exact moment a high-speed train passes over it, the G77-F150 is the only professional choice.

Available Models

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Specifications

Nominal Resistance
120 Ω or 350 Ω
Gauge Factor
Approx. 2.0
Strain Range
±3% (30,000 µε)
Operating Temp
-75°C to +200°C
Carrier Material
Polyimide / Epoxy
Fatigue Life
> 10^6 cycles at ±1000 µε
Grid Material
Constantan or Karma alloy