VEGA POINTRAC 31 8_16 mA_HART - four-wire With SIL qualification - Manual (Page 21)

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
defined 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 qualification
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
defined safe status
•
Determination of the failure probability of the defined safety func-
tion
•
Reliable parameterization with non-safe user environment
•
Recurring function test
The SIL qualification of components is specified in a manual for func-
tional safety (Safety Manual). Here, you can find 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 specifications in the Safety Manual.
The following inputs/outputs are permitted:
•
Relay output
Additional characteristics
and requirements