Category 3 Architecture
A redundant, dual-channel circuit structure in which the safety function is not lost because of a single fault. Some of the faults are also detected; however, accumulated faults can lead to loss of the function. For radio-controlled crane stopping, this architecture and performance level d are the common target.
The essence of the structure is two independent channels. Each channel can execute the stop command on its own; even if one fails, the other stops the machine. Cross monitoring is usually added on top, so the channels compare each other's state and report an inconsistency as a fault.
- Typical implementation: an emergency stop button with two positively opening contacts, a dual-channel safety relay and two separate contactors.
- Auxiliary contact monitoring: the normally closed auxiliary contacts of the contactors are wired in series to detect welding.
- Its limit: if undetected faults accumulate, protection can be lost; periodic testing is therefore necessary.
A radio remote control set with relay contact outputs does not build this architecture on its own; you create the redundancy in the panel. Instead of relying on the remote control output alone, guarantee the critical stop over a second independent path as well and test the function at defined intervals.
The context in which this term is used: Wireless Crane Remote Control Selection Guide