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SEMI S2-0703a E © SEMI 1991, 2004 84 R14-8.3.1 Use of Fail-to-safe Equipment C ontrol Sys tems with Con ventional Safe ty Technology — Equi pment manufacture rs can achieve fu nctional safety by the use of hardwired circ…

SEMI S2-0703a

immediately achieve a safe condition. An FECS

consists of sensors, logic systems and final elements as

shown in Section R14-11. Replacing an existing

electromechanical system with a safety controller does

not provide a safe system. Sensors and final elements

have to be considered as well.

R14-8.2.3 Safety Requirements – The FECS should be

suitable for SIL1 to SIL3 safety integrity level in

compliance with IEC 61508 or control categories 2 to 4

in compliance with ISO 13849-1 (EN 954-1). The

required safety performance requirements will be

determined in the system safety risk assessment. For

application assessment, local authorities and notified

bodies should request a safety handbook and

certification according to IEC 61508 or ISO 13849.

The safety-related system and its components should be

validated to ensure it fulfills the safety requirements

(SIL, CAT) determined from the risk analysis.

R14-8.2.4 Principle Of The Safety Functions — The

FECS executes safety functions to bring the equipment

into a safe state or to maintain it in a safe condition

when a hazardous event occurs. The safety function for

a production process can be realized using a user safety

function or a fault response function. The safe state can

be achieved by de-energizing the output modules.

R14-8.2.5 Communications — Non-safety-related and

safety-related communications between an industrial

controller and I/O modules should pass through a

standard network system or a safety network system in

sequence or through a combined network system (see

Figures R14-2-R14-7). Bridges, routers and repeaters

can be used in either standard networks or in safety

networks to adapt the network topology to the

individual layout of production process and equipment.

R14-8.3 Basic Topologies — Sections 7.3.1 through

7.3.3 describe examples of network-based architectures

that are capable of achieving a FECS. The suppliers

should take into account performance, timing, ease of

use, and other factors when selecting an architecture

type.

NOTE 8: These examples are not represented to be all-

inclusive.

SEMI S2-0703a

R14-8.3.1 Use of Fail-to-safe Equipment Control Systems with Conventional Safety Technology — Equipment

manufacturers can achieve functional safety by the use of hardwired circuits. Such hardwired circuits are realized

with terminals, electromechanical or electronic safety relays, and contactors. The relays would be certified for use

in CAT 4 applications according to ISO 13849. In Figure R14-2, a standard industrial controller is used with

standard I/O over a standard network to provide for the non-safety aspects of the machine and to provide diagnostics

and visualization of the hardwired safety functions.

Figure R14-2

Fail-to-safe Equipment Control System with Conventional Safety Technology

SEMI S2-0703a

R14-8.3.1.1 Use of Fail-to-safe Equipment Control Systems with Dual Networks for Standard and Fail-to-safe

Communications and Combined Controllers — Figures R14-3 and R14-4 are dual network systems with control of

the non-safety functions remaining the same as in Fail-to-safe Equipment Control Systems with Conventional Safety

Technology. Safety functions, however, are achieved using FECS with safety-related information and control

managed over a separate dedicated safety network.

Figure R14-3

Fail-To-Safe Equipment Control System with Dual Network for Standard and Fail-To-Safe Communication

and Separated Standard and Safety Controllers