VEGA VEGAPULS series 60 Recurring function test - Manual (Page 3)

1 About this document
The recurring function test serves to check the safety function and
reveal possible undetected, dangerous failures (λ
du
). The functional
capability of the measuring system has to be tested in adequate time
intervals. It is the user's responsibility to select an appropriate type of
testing. The time intervals are subject to the PFD
avg
-value according to
the specifications in the Safety Manual (SIL).
With high demand rate, a recurring function test is not requested in
IEC 61508. The functional efficiency 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 effect of the redundancy
through recurring function tests at appropriate intervals.
This supplementary information applies to measuring systems con-
sisting of radar sensor VEGAPULS series 60 in two-wire and four-wire
4 … 20 mA/HART versions:
VEGAPULS 61, 62, 63, 65, 66, 67, 68
Valid hardware and software versions:
Serial number of the
electronics
Sensor software
VEGAPULS 61, 62, 63,
65, 66 > 13978716 from version 3.22 up to
version 3.80
VEGAPULS 61, 62, 63
with increased sensitiv-
ity > 14165303 from version 3.25 up to
version 3.80
VEGAPULS 67, 68 > 14165303 from version 3.25 up to
version 3.80
With this supplementary information you can carry out a recurring
function test of VEGAPULS series 60 level sensors without dis-
mounting the instrument or moving the product level to the switching
point.
With this procedure, 88 % or 96 % of all dangerous undetected
instrument failures (λ
du
) are detected (DC
Proof
).
The described function test fulfils the requirements according to SIL.
If you have already created a sensor documentation during setup, you
can check the sensor at a detection rate of 96 % of all dangerous
undetected failures.
The remaining dangerous undetected failures are 11 FIT.
FIT = Failure In Time (1 FIT = 1 failure/10 9
h)
Why a function test?
Scope
Fault detection rate λ
du
96 %
Recurring function test • for VEGAPULS series 60 3
1 About this document
36553
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EN
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