Meggitt vibro-meter SpeedSys300 ODS301, Руководство пользователя

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Document reference MAODS301/E USER MANUAL
Edition 4 - May 2022 SpeedSys300 ODS301 overspeed detection system
3 - 7
Installation considerations
INSTALLATION OF A SPEEDSYS300 ODS301
3.2.5 Voting logic
To help ensure extra safety for and/or availability of rotating machinery, SpeedSys300
ODS301 modules can be combined to create different external voting logic structures, as
required.
More specifically, the SIL 2 design of the SpeedSys300 ODS301 module is SIL 3 capable
when used in a redundant 2oo3 architecture. To implement the 2oo3 voting logic required by
SIL 3 safety applications, the safety relay outputs from three SpeedSys300 ODS301 modules
can either be wired directly together or they can be connected to an external system such as
a safety PLC so that the required logic is evaluated before initiating a shutdown (“trip”) of a
machine.
For example, a SIL 3 overspeed solution for gas turbines uses 3 × SpeedSys300 ODS301
modules configured with external 2oo3 voting logic.
It is important to note that hardwiring the voting logic structure by wiring SpeedSys300
ODS301 module safety relays directly together avoids the introduction of interposing relays
or tailing PLCs, which would inevitably add failure modes to the whole chain, negatively
affecting the calculations for the SIL safety level and therefore the overall reliability.
For SIL safety loops, the use of the safety relays – relay 1 and relay 2 – is mandatory.
While technically, it is possible to use the additional (non-safety) relays – relay 3 and relay 4
– for 1oo2 and 2oo2 voting structures, these are not SIL rated. Accordingly, voting logic
configurations involving the non-safety relays are covered further in this manual and are at
the user’s discretion.
It is not recommended to mix differently numbered relays in one voting structure.
The below voting structure designations are regarded from a safety point of view.