Search for:
Mechatronic paths with inverted safety mechanisms
Explanation:
Section 5 (risk analysis) of the MSR form is searched through for error detections and error responses which are linked to each other in the wrong order.
Incorrect linkage order is available if an error response is placed before an error detection in the failure net (failure graph) in the direction of effects.
Example:
Abbreviations:
- The example demonstrating how the described quality rule (QR) works has the structure shown above. The contained failures and safety mechanisms are linked with each other as shown in the failure net below.
- The described QR searches for error detections and error responses that are linked to each other in the wrong order. That is the case if an error response is placed before an error detection in the failure net (failure graph) in the direction of effects.
The QR search algorithm starts from the focus failure (in our case: BF) and works through the error paths in the direction of effects and always searches for pairs of error detection and error response or error response and error detection. If the order is wrong within a found pair, the pair is marked as a hit and the search is continued for another pair in the same error path. If the order of a found pair is correct, no hit is registered, but the search is continued.
- The described QR can only be performed in the MSR form (risk analysis (step 5)). Therefore, the QR search result is displayed in the MSR form. The form that has the focus failure BF, looks as follows for our example after the QR search run:
Search result: 
If you make use of the above failure net, it becomes apparent that the pair of safety mechanisms “Er Resp 1 – Er Det 1” in the second failure net branch is in incorrect order and is therefore marked as a hit in the search result.
The error response Er Resp 5 following that pair in the failure net is not included in the search result because it is not part of a new pair of safety mechanisms linked in the wrong order.
Finally, the fifth failure net branch includes the pair of safety mechanisms “Er Resp 4 – Er Det 4”, which also has an incorrect order and is therefore also listed in the search result.