Vega VEGAPULS 61, Safety Manual

Page: 5 / 16

A ccording to IEC
61511
-
1
, paragraph
11
.
4
.
4
, the failure
tolerance
HFT
can be reduced by one for proven
-
in
-
use
subsystems if the following conditions are met :
l
T he instrument is proven in use
l
O nly process - relevant parameters can be modi fi ed on the
instrument ( e . g . measuring range , current output in case of
failure …)
l
T
he modi fi cation of these process
-
relevant parameters is
protected ( e . g . password , …)
l
T
he safety function requires less than
SIL
4
T
he assessment of the modi fi cation management was part of
the proof for " P roven in use " .
1
.
2
P lanning
T he measuring system generates on the current output a
signal between
3
.
8
m A and
20
.
5
m A corresponding to the
level .
T his analogue signal is transmitted to a connected processing
unit to monitor the following conditions
:
l
E xceeding a preset level
l
F alling below a preset level
W hen the switching point set on the processing unit is
reached , a signal is outputted .
T
he safe state depends on the mode
:
M onitoring upper level M onitoring lower
level
S afe state E xceeding the switching
point
F alling below the
switching point
O utput current in safe
state
> switching point (-
1
% ) < switching point ( +
1
% )
F ailure current " fail low " <
3
.
6
m A <
3
.
6
m A
F ailure current " fail high " >
21
.
5
m A >
21
.
5
m A
T he current tolerance ±
1
% refers to the full measuring range
of
16
m A .
A safe failure is present when the measuring system switches
to the de fi ned safe state or the fault mode without the process
demanding it .
P
roven in use
S afety function
S afe state
F ault description
VEGAPULS series
60
-
4
…
20
m A / HART
5
F unctional safety
31338
-
EN
-
070510