The ECR (Electrical Contact Resistance) is an add-on to the standard MTM2 system. The electrical resistance is measured between the disc and the upper specimen (ball, pin or roller).
An electrical potential is applied to the ball.
When the upper specimen is fully separated from the lower specimen (disc), the ECR reading will be 100%. When direct metal-to-metal contact is made between the specimens, the contact will be a short circuit and the ECR reading will be 0%.
During a test, the lubricant between the specimens is normally non-conductive, therefore the ECR signal (value between 0 and 100%) indicates the surface interaction between the specimens. This is particularly useful when studying additive performance in the mixed and boundary lubrication regimes. The ECR signal has proven valuable in the study of scuffing by detecting the sudden film collapse at the onset of scuffing.