Vega POINTRAC 31 8_16 mA_HART - four-wire With SIL qual Bedienungsanleitung PDF herunterladen (Seite 21)

6 Functional safety (SIL)

POINTRAC 31 • 8/16 mA/HART - four-wire

43388-EN-131119

6 Functional safety (SIL)

6.1 Objective

In case of dangerous outages, processing facilities and machines can

cause risks for persons, environment and property. The risk of such

outages must be judged by the plant operator. Dependent thereon are

measures for risk reduction through error prevention, error detection

and fault control.

The part of plant security depending on the correct functioning of

safety-related components for risk reduction is called functional

safety. Components used in such safety-instrumented systems (SIS)

must therefore execute their intended function (safety function) with a

denedhighprobability.

The safety requirements for such components are described in

the international standard IEC 61508, which sets the measure for

unique and comparable judgement of instrument safety and hence

contributes to worldwide legal certainty. Depending on the degree

of required risk reduction, we distinguish between four safety levels,

from SIL1 for low risk to SIL4 for very high risk (SIL = Safety Integrity

Level).

6.2 SILqualication

When developing instruments which can be used in safety-instru-

mented systems, the focus is on avoiding systematical as well as

determining and controlling random errors.

Here the most important characteristics and requirements from the

perspective of functional safety according to IEC 61508:

•

Internal monitoring of safety-relevant circuit parts

•

Extended standardization of the software development

•

In case of failure, switching of the safety-relevant outputs to a

denedsafestatus

•

Determinationofthefailureprobabilityofthedenedsafetyfunc-

tion

•

Reliable parameterization with non-safe user environment

•

Recurring function test

TheSILqualicationofcomponentsisspeciedinamanualforfunc-

tionalsafety(SafetyManual).Here,youcanndallsafety-relevant

characteristics and information required by the user and planner for

planning and operating the safety-relevant system. This document is

attached to each instrument with SIL rating and can be also retrieved

via the serial number search on our homepage.

6.3 Application area

The instrument can be used for level detection or level measurement

of liquids and bulk solids in a safety-related system according to

IEC61508.TakenoteofthespecicationsintheSafetyManual.

The following inputs/outputs are permitted:

•

Relay output

Additional characteristics

and requirements

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