KROHNE OPTISWITCH 3x00C Transistor SIL EN - Manual (Page 8)

1 .6 Recurring function test
The recurring function test is used to check the safety function,
to detect possible non-recognisable, dangerous faults. The
function of the measuring system must be checked in
adequate intervals.
The operator is responsible for choosing the type of check.
The time intervals depend on the selected PFD
avg
value
according to chart and diagram in paragraph "Safety-related
characteristics".
With high demand rate, a recurring function test is not
requested in IEC 61508. The function of the measuring system
is demonstrated by the frequent use of the system. In double
channel architectures it is a good idea to verify the redundancy
through recurring function tests at appropriate intervals.
The test must be carried out in a way that verifies the flawless
operation of the safety functions in conjunction with all system
components.
This is ensured by a controlled reaching of the response height
during filling. If filling up to the response height is not possible,
then a response of the measuring system must be triggered by
a suitable simulation of the level or the physical measuring
effect.
The methods and procedures used during the tests must be
stated and their suitability must be specified. The tests must be
documented.
If the function test proves negative, the entire measuring
system must be switched out of service and the process held
in a safe state by means of other measures.
In the double channel architecture 1oo2D this applies
separately to both channels.
1 .7 Safety-related characteristics
The failure rates of the electronics, the mechanical parts of the
transmitter as well as the process fitting are determined by an
FMEDA according to IEC 61508. The calculations are based
on component failure rates according to SN 29500. All values
refer to an average ambient temperature during the operating
time of 40 °C (104 °F).
General
Basics
8 OPTISWITCH series 3000 • - transistor (NPN/PNP)
Functional safety
32744
-EN
-080414