BCU 480 · Edition 03.16l
81
Glossary
11 .10 Main gas valve V2
The start fuel flow rate for the main burner is released
by main gas valve V2. It opens when the safety time on
start-up t
SA2
starts to elapse. It remains open until the
burner is switched off again by a controlled shut-down
or fault lock-out.
L1 (L1)
N (L2)
PE
1 2
PE
N1
N1
s
s1
V1 V2
C
N
S
M
L
µC
l
N1
v1
c2
88
c1
N1
v2
V1
V2
F1
230V~
max. 2 A,
253 V
I
Z
30 31 32 33 34 35 36 37
DI
50 51
l
38
F3
(BCU 480..C)
40 41 42 43 44 45 46 47
UVS
1
2
3
P
5
6
7 8
11
9 10
12 13 14 15
25 26 27
18 19 20
22
24
PE
7 8 9 10
24 25
PE
7
8
9
24
Test
O
I
BCU 480
ϑ
1
ϑ
2
A
23
2
1
16 17
28 29
21
3 4
11 .11 Continuous operation
The gas burner runs continuously for more than 24
hours.
11 .12 Air valve
The air valve can be used
– for cooling,
– for purging,
– to control the burner capacity in ON/OFF mode and
in High/Low mode when using a pneumatic air/gas
ratio control system.
11 .13 Diagnostic coverage DC
Measure of the effectiveness of diagnostics, which may
be determined as the ratio between the failure rate of
detected dangerous failures and the failure rate of total
dangerous failures
NOTE: Diagnostic coverage can exist for the whole or
parts of a safety-related system. For example, diagnos-
tic coverage could exist for sensors and/or logic system
and/or final elements. Unit: %.
from EN ISO 13849-1:2008
11 .14 Mode of operation
High demand mode or continuous mode
Operating mode, where the frequency of demands for
operation made on a safety-related system is greater
than one per year or greater than twice the proof-test
frequency
from EN 61508-4:2001
11 .15 Safe failure fraction SFF
Fraction of safe failures related to all failures, which are
assumed to appear
from EN 13611/A2:2011