Looking for information on "Checked Redundancy"


Thread Starter

Joe Malter

I'm experienced in using PLC redundancy (AB, Modicon and Sq.D) and I'm familar with triple redundant systems like Triconix but I'm not familar with Checked Redundancy. I understand it is required in the transportation industry with trains and people movers.

Does anyone know where I can find reference information and possible examples on the subject?
Checked Redundancy or Self checking circuitry is called for in the European standard EN 60204 and most safety product manuals describe
how to build these and how to assess the required level of redundancy and self checking. Basically the self checking circuits require monitoring of the redundant contacts to ensure that both contacts respond in a minimum time in both directions. Most safety controllers have this built right in and typically will look for the contacts to close or open together in 300ms or
less. If they do not perform as expected the controller will de-energize the MPCE control relays which will disable the machine. Go to www.sti.com and view their online manuals. They describe how to evaluate and build control reliable circuits for the different levels of safety. I find it a good reference for this topic.