Strain Gauges - Load Cells, Engineers' Handbook

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Sensors: Force

Force

Load Cells / Force Transducers

Tension Load Cell

Load Cells are intended for determination of static or dynamic tensile and compressive loads and come in many different forms including compression, tension, simple beam and single point. Force transducers can be used as load cells, but can also be used in weighing applications and measuring compression or tension. Load cells can be built utilizing either transducers, LVDTs, strain gauges or piezoelectric sensors.

Strain Gauges

Strain gauges are used for the measurement of tensile and compressive strain in a body and can therefore pick up expansion as well as contraction. Strain is caused in a body by internal or external forces, pressures, moments, heat, or structural changes in the material. In general, most types of strain gages depend on the proportional variance of electrical resistance to strain: the piezoresistive or semi-conductor gage, the carbon-resistive gage, the bonded metallic wire, and foil resistance gages.

The bonded resistance strain gage is by far the most widely used in experimental stress analysis. They typically consist of a grid of very fine wire or foil bonded to the backing or carrier matrix. The carrier matrix attaches to test specimens with an adhesive. When the specimen is mechanically stressed (loaded), the strain on the surface is transmitted to the resistive grid through the adhesive and carrier layers. The strain is then found by measuring the change in resistance.

The bonded resistance strain gage is low in cost, can be made with a short gage length, is only moderately affected by temperature changes, has small physical size and low mass, and has fairly high sensitivity to strain.