Hello,

How do safety relays monitor whether the internal contacts or an external positive-guided contactor contacts have welded during normal operation?

I understand that when the system is powered down, a restart will be prevented due to the welded contacts.

Hello Elec-Eng;

Here is a very general explanation of Safety relays monitoring functions, provided by the PLC Academy.

https://www.plcacademy.com/safety-relay/

I have extracted the more relevant section from this article and you will find it in the screenshot below.

For more detailed brand information you should look up safety relays manufacturer's sites, such as Pilz, Sick, Siemens, Rockwell, ABB...

Hope this helps,

Daniel Chartier