Designed to be embedded in concrete for measuring strains due to imposed loads.
It is welded into and becomes an integral part of the existing rebar cage. (Sister bars are tied-in, not welded.) Particularly applicable for pours where placing of concrete is remote and uncontrolled, typically in diaphragm walls and deep piles.
Rebar strain meters are usually installed in pairs on either side of the neutral axis. The extensions are long enough to ensure perfect contact with the surrounding concrete so that measured strains inside the steel are equal to the strains in the surrounding concrete.