P-9903 Loop Relay Module is 24VDC powered. The input and output of loop signal are insulated to ensure transmission of detector signal which enhances interference-resistant ability of the system and prolongs the loop distance. P-9903 is mainly used in applications where strong electromagnetic interference exists or where the loop needs to be extended to longer than 1000m. The relay module consists of a transmitter circuit, a receiver circuit, and an isolated power supply. Optocoupler isolation technology is used between the transmitter and receiver circuit.