The theory of resistivity involves the ways that materials conduct or resist the flow of electricity and plays an important role in the study of metals and semiconductors. Every metal alloy has its unique level and characteristics of electrical resistivity. Within the same alloy specimen, resistivity varies with the composition of the material and internal structure and/or defects.

Quality measurement of a laser seam weld

Differences in resistivity values provide practical means for NDT inspection and process control including :

Measurement of material thickness
in block mode, as well as detecting flaws

Quality measurement of five
independent spot welds

Sprayed Coatings
(metal to metal, metal to non-metal)

NDT Automation's M100A Resistivity Meter provides rapid, accurate measurements of electrical resistivity that yield either bulk or surface characteristics of the material components being tested.

The M100A takes advantage of a special form of ohm's law by generating a pair of rapidly reversing direct current pulsing through the two outer probes of a four-point assembly placed on a test specimen. Resulting voltage measurements, taken from the inside points of the probe, are electronically converted to resistivity values for interpretation. This permits rapid evaluation of specific material characteristics. The resulting data is absolute (unlike most other NDT techniques).

Readings can be stored in a PC for automated data recording and / or process control. Effective depth of current penetration is controlled by changing probe configuration. The key to utilizing this technology for non destructive evaluation is the change in resistivity values from one sample to another due to material processing or the presence of defects.