Spring Deformation Gauge for Measuring Local Deformations in Triaxial Apparatus

Table 1

Issues associated with LVDTs and LDTs.

Device	Critical issues (disadvantages/limitations)
Linear variable displacement transformers (LVDT)	(i) Alignment of the transducer inevitably leads to stiff connections that may affect sample behaviour.; (ii) Bulky; (iii) Potential friction between the moveable iron core (armature) and the internal cage housing the electromagnetic coils, either by misalignment or due to specimen barrelling.; (iv) Special arrangements are required to measure radial strain; (v) Unless it is of the unguided type, damage may occur if the LVDT goes out of range.; (vi) Relatively expensive
Local deformation transducers (LDT)	(i) Nonlinear output; (ii) Friction between the gauge strip and the pin connection unto the specimen can change the boundary conditions normally assumed during calibration; (iii) Nondurable; (iv) Can get damaged during a test when it goes out of range unless a complex mechanism is used to undo it