The purpose of this research is to propose a method for evaluating the time-dependent corrosion behavior of carbon steel plates using an atmospheric corrosion monitor (ACM) corrosion sensor consisting of a Fe/Ag-galvanic couple. Atmospheric exposure tests were carried out on steel plates for periods of 6, 12, and 24-months on the island of Okinawa in Japan. The Specimens were mounted on racks at angles of 0, 45 and 90 to the horizontal to obtain corrosion data in various corrosive environments. In addition, the environments of the skyward- and groundward-facing surfaces of the specimens were monitored using ACM sensors. The sensor outputs were recorded during the exposure tests.