A potentiostat data link (PDL) unit is provided which can remotely monitor the formation and growth of cracks in metal structures. A PDL includes a sealed box containing two or more modified potentiostats, a power supply, a CPU, a memory device, and computer networking capability. The PDL can be mounted in a remote, difficult-to-access location. Each potentiostat has a lead to a sensor affixed to a structure to be analyzed for the presence of growing cracks due to metal fatigue in a metal structure.