Extensometer

The extensometer is an instrument designed to measure the distance separating two fixed points by determining extension or contraction of a connecting element under stress which is temporarily or permanently attached to the fixed points.

The first such instrument was designed to measure deformation of iron rods during fatigue testing (Huston 1879). There are other instruments allowing determination of distance between fixed points by direct distance measurements (e.g., precision tape; laser distance meters; electronic distance meters) without using connecting element under tension.

Repeated readings are required to detect changes of the connecting element length which indicates relative displacement of the fixed points with respect to each other. Determination of their movement vector or total displacement requires additional information which cannot be provided by the extensometric measurements alone but is largely affected by the...