PLEXUS EXAMPLE · 06

SIF register vs Basis of Design

Nine safety functions checked against the BoD: initiators, final elements, SIL targets and test basis, with conflicts flagged for review.

Input

SIF REGISTERACD-SRS-0001

Safety Requirements Specification, SIF register

Revision: Rev A
Functions: 9
Source: SRS working copy

BASIS OF DESIGNACD-BOD-0001

Basis of Design & Operation/Control Philosophy

Revision: Rev 0
Section: 6.5 Safety instrumented functions
Basis: IEC 61511, LOPA targets

The source documents are not shown: safety requirement specifications stay inside your project. The check below runs on a hypothetical plant (ACD), presented the way consistency results arrive.

What Plexus does

01Reads the SIF register and the BoD SIS table into one structure.
02Aligns each function: initiator and voting, final elements, SIL target, proof-test basis.
03Marks each field pass, conflict or check.
04Flags the conflicts; the engineer confirms and routes changes through management of change.

Output

0 / 36 checksrun first, then export

This animation illustrates the Plexus workflow on a hypothetical plant (ACD). In the product, consistency checks run server-side and every value keeps provenance to its source document; an engineer reviews and SIS changes follow management of change.

Source documents: ACD-SRS-0001 Rev A and ACD-BOD-0001 Rev 0, hypothetical plant

Safety instrumented function	Initiator (voting)	Final elements	SIL target	Proof test
SIF-101Heater overtemperaturesafe state: Fuel isolated, coil protected	TSHH-6003 (1oo2)conflictBoD: TSHH-6003 (2oo3 RTDs)Register carries 1oo2 voting; the BoD LOPA basis is 2oo3. The PFD claim behind SIL 2 rests on the voting architecture.	SDV-6001, SDV-6002 close; XV-6003 openspassBoD: SDV-6001, SDV-6002 close; XV-6003 opens	SIL 2passBoD: SIL 2	12 months + 6-month partial strokepassBoD: 12 months + 6-month partial stroke
SIF-102Low hot-oil flowsafe state: No firing without oil flow	FSL-6006 (1oo1)passBoD: FSL-6006 (1oo1)	SDV-6001/6002 close; XV-6003 openspassBoD: SDV-6001/6002 close; XV-6003 opens	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-103Flame failure / fuel low pressuresafe state: Burner trip (BMS)	BSL-6007A/B (1oo2)checkBoD: BSL-6007A/B (1oo2) or PSL-6005The BoD lists PSL-6005 low fuel pressure as an initiator; the register carries only the flame scanners. Confirm the BMS package scope boundary.	SDV-6001/6002 close; XV-6003 openspassBoD: SDV-6001/6002 close; XV-6003 opens	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-104V-301 high pressuresafe state: Feed and reaction heat cut	PSHH-3005 (1oo1)passBoD: PSHH-3005 (1oo1)	SDV-2001 closes; TV-2102 driven closedpassBoD: SDV-2001 closes; TV-2102 driven closed	SIL 1conflictBoD: SIL 2Register predates the LOPA revision that raised the target to SIL 2. Verification, proof-test and hardware claims all change with it.	12 monthscheckBoD: 12 months + 6-month partial strokeThe BoD adds a 6-month partial stroke of the SDV online; the register carries the annual test only. Confirm the test plan.
SIF-105T-501 overfillsafe state: Tank inlet isolated	LSHH-5002 (1oo1)passBoD: LSHH-5002 (1oo1)	SDV-5001 closespassBoD: SDV-5001 closes	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-106C-401 high pressuresafe state: Reboiler heat cut	PSHH-4006 (1oo1)passBoD: PSHH-4006 (1oo1)	TV-4007 driven closedpassBoD: TV-4007 driven closed	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-107Reactor overtemperaturesafe state: Feed and heat cut	TSHH-2104 (1oo1, dual element)passBoD: TSHH-2104 (1oo1, dual element)	SDV-2001 closesconflictBoD: SDV-2001 closes; TV-2102 driven closedThe hot-oil heat-cut element TV-2102 is missing from the register; feed isolation alone does not remove the reaction heat.	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-108T-101 low-low levelsafe state: Pump protection	LALL-1003 (1oo1)passBoD: LALL-1003 (1oo1)	P-101A/B trippassBoD: P-101A/B trip	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months
SIF-109T-501 low-low levelsafe state: Pump protection	LALL-5003 (1oo1)passBoD: LALL-5003 (1oo1)	P-501A/B trippassBoD: P-501A/B trip	SIL 1passBoD: SIL 1	12 monthspassBoD: 12 months

Manual: 2-4 hours
With Plexus: 15-30 min review (estimate, nine-function register against the BoD SIS table)

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