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It is a potential critical event who can be hazard for Machinery Safety.
Logical connection of the interlocking devices are for contacs normally closed in series, and for contacts normally opened in parallel. In case of series links the trouble of a single element can be hidden from devices linked in series to the same one control system.
In case of opening of relative safety guards, relay will stop the machinery in the safety area. The operator will supposedly try to close the safety guards and reset through reboot, without success due to the trouble signal is saved from the control system. After the checking of remainder contacts, and opening the first one, the relay will be cheated and will read the opening of series interblock‘s healthy contacts, therefore it will restore safety status and reboot the system.
The operator will be chated while the safety system will load a trouble not identified, who will compromise the safety function and so will increase the risk at the next access.
If it isn’t any possibility to modify the logical link, it is suggested to insert into the user manual a monthly check for Performance Level D or yearly for PL E.