0
Answered

Redundant modules

Greg R 2 years ago in Master modules / MC4x updated by Gustav Widén (System support) 1 year ago 2

I am trying to design a system with redundant MC43s controlling the same components on their COUTs and DOUTs. Only one module would output at a time. Could this be accomplished without using relays? Can Diodes be used to prevent one backfeeding into the other? What is your suggestion?

I have been involved in design and support of redundant systems for many, many, years, as used on steam boilers for pulp industry, electric power generation, etc.  The inputs can be paralleled, and monitored simultaneously, but never the outputs.  We used a separate monitoring circuit (custom designed PCB) to monitor health and know when to transfer between primary and secondary control system output drivers.  You just can not parallel outputs like this, with out them "fighting" and faulting due to backfeeding, etc.  


Answered

Only one COUT or one Digital out HS+LS can be connected to the coil. 

There is a related discussion here on what diagnostic errors that gets triggered if one tries to connect something in parallel to the outputs https://forum.iqan.se/communities/1/topics/1479-overload-on-mc43fs-dout-hsls-channel