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4.5. Operating behaviour of the monitoring equipment
For the evaluation of the monitoring a superior control system, which is in accordance with the functional
safety requirements of IEC/EN61508, must be available. The control system must be capable of carrying out
a fault analysis according to the capacity of failure in connection with the operational condition of the sound-
er. The following dependencies between operational condition and capacity of failure are therefore possible.
Please also take note of the possible switching status as shown in Fig. 7 and Fig. 8.
It is assumed that the monitoring equipment is supplied with operational voltage at least 1s before switching
the sounder channel on and the condition of the alarm output is checked 0.5s after switching on at the earli-
est. This procedure is an integral part of the automatic test function, as described in section 4.7.
a) Switching on the power supply of the sounder channel in a fault free condition results in the control-
ling of the MOS relay (the output of the MOS relay is low resistance). This takes place with a delay of
0.2 seconds. This is on the condition that a tone has been selected with help of the DIP switch for
the tone selection or a respective tone has been activated from the 'external tone selection' and the
monitoring circuit is attached to the power supply. If the capacity of failure has not become low-
resistance after this time then a fault has occurred in the supply of the sounder channel, in the
sounder channel itself or in the monitoring equipment. If the capacity of failure is already low-
resistance before hand, then there is a conductor end or a malfunction in the monitoring circuit.
b) If the operational voltage of the sounder channel is switched off, a fault message is given via the
fault alarm relay with a delay of 0.2s to 2.5s. With an uninterrupted sounding, a reaction of the alarm
relay of >0.2s can be expected. The longer delay can result in tonal pauses in uninterrupted sound-
ing when switching off.
c) If tones are automatically ended by the sounder (such as with tones 26 and 98, for example) then a
fault is also reported after 4s. In this case, the control must take into account the procedure of the
tonal generation (60s) and reset it.
d) If, during operation of the sounder channel, it is the case that the sounder remains off without the
operational voltage for the sounder channel being switched, the alarm output becomes high-
resistance after a maximum delay of 4s and therefore a fault is reported.
e) The minimum duration of an alarm is 5s. Only after this time has lapsed does it switch back to the
normal monitoring mode.
4.6. Time dependencies
Fig. 7
Function time diagram
Tone
Operational voltage
Sounder channel
Operating voltage
Monitoring circuit
Alarm output
* depending on the tone
for non-interrupted tones 0,2s
for long tone intervals up to max.
2,5s
** valid only for the independent
ending of tones 26 and 98
