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Starting alarms and similar uses are architectures that can normally be attributed to the 'high demand mode'.
The acoustic function must be tested immediately before switching on the machine or before entering the
dangerous condition.
Safety parameters for starting alarms
T
ProofTest
5 10
Years
PFD
mean
1,68 x 10
-3
3,36 x 10
-3
(1/
requirement)
PFH
G
7,7 x 10
-8
7,7 x 10
-8
(1/h)
SFF 98,98
%
DC 0
%
MTTR 48
h
λ
DU
diagnosis switch
76,5
Fit
λ
S
Complete
7456
Fit
HFT 0
Suitability of the system for use in safety chains until
SIL 2
4.4.2. Use as an acoustic warning system in one-channel version
The function of the acoustic warning system is to be assessed as a safety function in the use as a warning
system after recording dangerous conditions. A measurement records a dangerous condition and introduces
the safe condition by controlling the acoustic warning system (personnel/operator is warned).
Note: The warning of people is a voluntary measure as it requires willing handling of one or more people.
This architecture only corresponds to the requirements of the European Machinery Directive if, according to
state-of-the-art technology, no constructive safety or other voluntary measure is possible to reach a safe
condition.
The diagnosis can only be taken into account if there is regular, automated function checking, the minimum
interval of which must be in accordance with approx. ten to one hundred times the requirement rate accord-
ing to IEC/EN61508. This possibility is only available in low demand mode and is further described and eval-
uated in section 4.4.2.2.
The acoustic warning system with diagnosis function is implemented as follows:
a) A measurement (input (1), logic (2)) records a dangerous condition and activates the acoustic warn-
ing system (output (3))
b) The diagnosis (4) monitors the function of the acoustic warning system and reports OK to a superior
control system (5)
c) If an OK message takes place, then the superior control system (5) introduces the safe condition via
other measures (6).
Fig. 6
Fig. 6. In section 4.4.2.2 the sounder partial systems (output - position 3) and diagnosis channel (diagnosis -
position 4) are evaluated. It should be noted that the sum of all PFH or PFD values must correspond to the
required safety integration level for the entire system.
Recording
(Input)
Evaluation
(Logic)
Output
(Output)
Diagnosis
(Output)
Superior
system
Output
1
2
3
4
6
5
