Main Gas Valve V2; Continuous Operation; Air Valve; Diagnostic Coverage Dc - Honeywell Krom Schroeder BCU 480 Manual

Burner control units
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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
s1
start-up t
starts to elapse. It remains open until the
SA2
F1
V1
V2
C
N
S
burner is switched off again by a controlled shut-down
or fault lock-out.
88
µC
5
6
PE
ϑ
DI
1

11 .11 Continuous operation

8 9
24
The gas burner runs continuously for more than 24
hours.

11 .12 Air valve

The air valve can be used
I
– for cooling,
Z
– 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.
BCU 480 · Edition 03.16l
N1
N1
N1
c2
c1
v1
v2
7 8
9 10
11
12 13 14 15
V1
V2
PE
7 8 9 10

11 .13 Diagnostic coverage DC

Measure of the effectiveness of diagnostics, which may
be determined as the ratio between the failure rate of
Test
detected dangerous failures and the failure rate of total
M
L
dangerous failures
NOTE: Diagnostic coverage can exist for the whole or
parts of a safety-related system. For example, diagnos-
1
s
tic coverage could exist for sensors and/or logic system
16 17
18 19 20
21
22
23
24
and/or final elements. Unit: %.
from EN ISO 13849-1:2008
max. 2 A,
253 V

11 .14 Mode of operation

High demand mode or continuous mode
A
Operating mode, where the frequency of demands for
operation made on a safety-related system is greater
ϑ
2
P
than one per year or greater than twice the proof-test
frequency
from EN 61508-4:2001
24 25

11 .15 Safe failure fraction SFF

Fraction of safe failures related to all failures, which are
assumed to appear
from EN 13611/A2:2011
1
UVS
2
3
(BCU 480..C)
40 41 42 43 44 45 46 47
F3
2
N1
l
25 26 27
28 29
30 31 32 33 34 35 36 37
BCU 480
l
38
50 51
L1 (L1)
N (L2)
PE
81

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