PURPOSE: To make possible the remote measurement of the corrosion prevention control measurement values at remote points automatically and inexpensively by converting the corrosion prevention control information of buried metallic pipes in substations to predetermined signals, injecting these to the metallic pipes, transmitting the same and extracting and receiving these signals in a master station.
CONSTITUTION: In a substation device 8 of a measurement point A, the potential difference between a buried pipe 1 and a reference electrode 16, that is, the potential to ground of the pipe 1 as measurement necessary for control of corrosion prevention is measured in a measuring part 17. The superposed AC components are removed and only the natural voltage or corrosion preventive potential is converted to a digital value which is then injected as pulse code current into the pipe 1 via a transmission part 13. On the other hand, the potential to ground between the pipe 1 and a receiving electrode 11 is detected in the receiving part 14 of a master station device 8 at a receiving point B, and the superposed pulsation is removed, so that only the pulselike change is inputted to a processing part 16. The substation number code of the measured value signal received is collated with a selecting part 15, and when it is accepted, it is printed in the processing part 16, whereby data are collected.