Hello,
I am a new member and have a question regarding old PLC systems. We are still using Modicon 484 PLC at work. The system uses discrete I/O modules with +/- 48VDC control voltage. Both voltage rails are individually fused. While performing load verification, a maintenance personnel pulled the negative rail causing the PLC to send a false signal causing inadvertent actuation of an end device. It is important to note that when pulling the positive rail fuse by itself, the system did not respond the same way.
What is the significance of the negative rail? why did the system behave abnormally when the negative rail fuse was pulled?
Thank you very much.
I am a new member and have a question regarding old PLC systems. We are still using Modicon 484 PLC at work. The system uses discrete I/O modules with +/- 48VDC control voltage. Both voltage rails are individually fused. While performing load verification, a maintenance personnel pulled the negative rail causing the PLC to send a false signal causing inadvertent actuation of an end device. It is important to note that when pulling the positive rail fuse by itself, the system did not respond the same way.
What is the significance of the negative rail? why did the system behave abnormally when the negative rail fuse was pulled?
Thank you very much.