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Automated independent backup system

This automated independent backup standalone safety instrumented system backs up current process control trip logic and meets the requirements of IEC 61511. The system includes an IEC 61508 logic solver that is functionally independent from the process control system, supplements existing logic and meets all appropriate safety standards.

February 10, 2010
DIAMOND-SIS automated independent backup (AIB) is alow-cost, standalone safety instrumented system (SIS) that backs up currentprocess control trip logic and meets the requirements of IEC 61511. The systemincludes an IEC 61508 logic solver that is functionally independent from theprocess control system, supplements existing logic and meets all appropriatesafety standards.

DIAMOND-SIS AIB provides high integrity and process

reliability. It is available in single, dual and triplicated channel

configurations with online diagnostics, testing and maintenance capabilities.

The single and dual channel systems are acceptable for SIL 2, while the

triplicated channel systemis certified by Factory Mutual to SIL 3. This means

that DIAMOND-SIS can meet the fault tolerance and PFavg requirements of any

application.

With its 5 A output rating, the system can de-energize

multiple final elements including motor control circuits and/or solenoid

operated valves. Local or remote manual reset ensures controlled process

restart after shutdown.

DIAMOND-SIS AIB is particularly useful with legacy control

systems that do not meet current SIS standards. Typically, during the early

days of digital control, users implemented safety logic within their process

control systems. Today, they do not want to impose SIS requirements or

management restrictions within the existing systems. Instead, they need an

independent backup safety logic system that connects easily to existing plant

equipment, meets all safety standards and requirements, and requires no

reprogramming of process logic. DIAMOND-SIS AIB fulfills all of those

requirements.

A single channel DIAMOND-SIS AIB system includes a

pre-mounted and wired DIN-rail signal isolator, a Model 340 logic solver, a

fuse block and five terminals ready to accept existing wiring. All components

are rated for -30 C to 75 C and Class I Div II operation, and meet the

mechanical integrity requirements of IEC 61511.

The system can typically be mounted in an existing DCS

marshalling cabinet, and the user wires the logic solver contacts in series

with the DCS contacts. The logic solver then independently backs up the trip

functionality of the DCS.

Each DIAMOND-SIS logic solver module can accept virtually

any analog input. Its two field adjustable trip points allow the process to be

shut down on high and/or low process variables, or to detect an out of range

signal fault. The number of inputs and the voting architecture – such as 1oo1,

1oo2,2oo2 or 2oo3 – can be adjusted to meet performance requirements. The

process shutdown signal from the logic solver can be sent to both the DCS, and

directly to a shutdown device such as a relay or solenoid.

The installation does not require any reprogramming of the

existing DCS. In addition, the installation cost of a DIAMOND-SIS AIB is 80%

less than that of an equivalent Safety PLC with the same number of loops.

Maintenance costs are also greatly reduced as it’s not necessary to purchase,

implementand renew programming software. The Safety Requirements Specification,

including Safety Integrity Level (SIL) verification documentation, can be

supplied as an option.

SIS-TECH

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