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4 Measurement Tutorials
Stress
Stress is a term used to compare the loading applied to a material with its ability to carry the load. Stress (σ) in a
material can not be measured directly; it must be computed from material properties and measurable quantities
such as strain and force.
Strain sensors
The metal foil resistance strain gage is by far the most widely used strain measurement sensor. It consists of a thin
metallic foil grid bonded to a thin insulating, adhesive backing. The resistance of the foil varies linearly with strain.
Strain in the test body is simply the ratio of the foil's strained to unstrained resistance: ε = ΔR / R.
Gage Factor (GF)
The Gage Factor (GF) indicates the sensitivity of a strain gage and is a measure of the fractional resistance change
per strain: GF = (ΔR / R) / ε. Devices with a higher gage factor will exhibit a greater resistance change per strain
applied.
Strain gages are available in various numbers and configurations of elements. The most common element is the
single gage form shown below. Multi-element strain gages, also called rosettes, are used to measure components of
strain in different directions. Two-element (90°) and three-element (45° or 60°) configurations are the most
common.
Common uses for strain gages
Strain gages are used to sense many types of physical parameters. Strain gages are primarily a force-sensing
device. Force is measured indirectly by measuring the deformation of a test body to a known applied force thus
producing a resistance change proportional to the applied force. Many other physical quantities can be measured
through force measurements. Common applications of strain gages include weight, pressure, flow, and level
measurements.
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Keysight DAQ970A/DAQ973A User's Guide
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