The invention provides a
large deformation extensometer, comprising a sensor, a regulating bar with a hook, a fixed bar, a scale distance limiting plate and a pair of an upper knife edge group and a lower knife edge group which are eudipleural and arranged at the upper part of the regulating bar and at the lower part of the sensor respectively; the
extensometer is characterized in that the sensor which is arranged at the lower part of the fixed bar and articulated with the hook at the lower part of the regulating bar is a draw out type displacement sensor; the draw out type displacement sensor comprises a box body, a steel
wire rope and a
coil spring type contracting mechanism A and an
encoder which are arranged in the box body; the
coil spring type contracting mechanism comprises a
clockwork spring shaft one end of which is fixedly connected with the box body, a spring plate capable of circuition arranged at an axis body and a disk
clockwork spring one end of which is fixed on a locating shaft and the other end of which is fixed in the inside cavity of the spring plate; one end of the steel
wire rope is fixed on the spring plate and led out after being sheathed and wound by a winding shaft which is in swing connection with the
encoder; the other led out end thereof is directly connected with the hook and forms a
large deformation extensometer automatic contracting mechanism with the hook at the lower part of the regulating bar by the hook.