TYPES AND WORKING PRINCIPLES

A strain gauge, as its name implies, is a thin extensoresistive (piezoresistive) or extensoelectric (piezoelectric) device which can be used for measuring the strain experienced by the surface of a solid. The terms "piezoresistive" and "piezoelectric", which are often indiscriminately used by many to refer to the functioning of strain gauges, should, in our view, be reserved to stress sensors only. The words "extensoresistive and extensoelectric" are believed to be more descriptive to infer strain gauges’ functionality and thus will be used here. Extenso means change in length of an element. All extensoresistive and extensoelectric strain gauges have been accurately calibrated using controlled gas gun impact tests.
In general, Dynasen offers two different types of strain gauges, 1) the uni-directional strain gauge with grid lines either parallel to its output leads (defined here as longitudinal) or with grid lines perpendicular to its output leads (called a lateral strain sensor) and 2) a Bi-directional model that combines both. The bi-directional strain gauge, provides the capability to simultaneously measure the sum of two orthogonal lateral strains. Such bi-directional gauge arrangement use a rectangular "spiral like" sensing grid having equal longitudinal and lateral strain sensivity.

The output of an extensoresistive strain gauge is typically expressed in terms of relative or fractional change of electrical resistance versus strain. Strain gauges are typically made part of a bridge arrangement and electrically excited using DC or pulse schemes. See Dynasen's excitation sources.

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UNIAXIAL STRAIN GAUGE

The classical construction of a (extensoresistive) strain gauge consists in a thin Constantan (Cu:55%, Ni:45%) grid-like sensor that is photo-etched and glued upon a thin polymer backing film. By properly cementing the backing film of the above arrangement upon the surface of a test sample, it thus becomes a means to infer the strain experienced by the surface from a simple resistance measurement. The above strain gauge, which can also be of a fully encapsulated construction, is called a uni-directional strain gauge as it primarily responds to the strain experienced by the sample in the direction of the element’s grid lines.

CONSTANTAN STRAIN GAUGES

MODELS CN4-50-EK ,CN2-50-EK. 50 OHM (UNI-DIR. LONG .& LAT..)

Dynasen’s strain gauges models CN4-5-EK and CN2-50-EK are uni-directional longitudinal and lateral 50-OHM gauges constructed identically to our Manganin gauges. The standard construction is longitudinal and utilizes 0.001 Inch-thick Kapton. Consult our price lists for standard element sizes. Please specify directionality (Long. or Lat.) of strain and lead length upon ordering.