The Importance of Relay and Programmable Logic Documentation

With increasing use of microprocessor-based relays, incorporating logic into relays has become more common. Traditional relay and control schemes used dc control schematics to describe how schemes functioned. The ability to see electrical paths aided technicians during testing and troubleshooting. As logic is incorporated into relays, the ability to visualize logic is important for complete testing and troubleshooting. This paper describes the need for documenting relay logic, highlighting the importance of testing, and understanding relay logic. The paper describes real-world examples of misoperations due to failure to fully test logic schemes, and it reviews several documentation methods.