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Version 17
Safe-E-
Stop™
User Guide
8.2.1 Single Channel Connections Example when using the COMM LOSS Relays
The following configuration combines the SIL3 function of the COMM LOSS relays with the systematic capability
of 3 provided by the E-Stop relays in a single channel configuration.
If a single PSD is always to be used, then use of the COMM LOSS relays will also provide additional status
information. Once one PSD is ‘LINKED’, it is placed into service as an additional E-Stop and the COMM LOSS
relays are closed. If a user fails to link their PSD and confirm that it is linked, it will not be detected and the
machine could be reset unless the COMM LOSS relays are wired in series with the E-Stop relays, this will enforce
the need for a single PSD.
However, each additional PSD will not make any further difference to the COMM LOSS relays;
if additional
users fail to LINK correctly and confirm LINK status, it will not be detectable via the COMM LOSS relays. If further
confirmation is required, it is possible to implement additional verification using the Ethernet bus data and a PLC
control system to ensure that one, two, or a minimum number of PSDs is linked for operation to commence. Once
linked, any PSD that has a COMM LOSS will cause the COMM LOSS and E-Stop relays to open.
Additionally, if the machine is to be run without a PSD connected at times, this will not be possible without either
overriding or not using the COMM LOSS relays, because their state will be open without a linked PSD.
The single channel connection method below will not provide protection against an external wiring fault.
Figure 12: MSD Typical Single Channel Connections When Using the COMM LOSS Relays
