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SIS-Tech has introduced Diamond-SIS automated independent backup (AIB), a low-cost, standalone safety instrumented system (SIS) that backs up current process-control trip logic.

The system, which meets the requirements of IEC 61511, includes an IEC 61508 logic solver that is functionally independent from the process-control system, supplements existing logic and meets all appropriate safety standards.

Diamond-SIS AIB 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 system is certified by Factory Mutual to SIL 3.

This means that the Diamond-SIS system can meet the fault tolerance and PFavg requirements of any application.

With its 5A output rating, the system can de-energise multiple final elements, including motor control circuits and/or solenoid-operated valves.

Local or remote manual reset ensures a controlled process restart after shutdown.

Diamond-SIS AIB is said to be 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 to existing plant equipment, meets all safety standards and requirements and requires no reprogramming of process logic.

Diamond-SIS AIB fulfils these requirements, according to the company.

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 -30C to +75C 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 analogue 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 a solenoid.

The installation does not require any reprogramming of the existing DCS.

SIS-Tech claims that the installation cost of a Diamond-SIS AIB system is 80 per cent less than that of an equivalent safety PLC with the same number of loops.

Maintenance costs are also reduced as it is not necessary to purchase, implement and renew programming software.

The Safety Requirements Specification, including SIL verification documentation, can be supplied as an option.

This makes Diamond-SIS AIB suitable for addressing low input/output SIS needs.

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